Month to Year Converter
Convert months to years with our free online time converter.
Quick Answer
1 Month = 0.083333 years
Formula: Month × conversion factor = Year
Use the calculator below for instant, accurate conversions.
Our Accuracy Guarantee
All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Month to Year Calculator
How to Use the Month to Year Calculator:
- Enter the value you want to convert in the 'From' field (Month).
- The converted value in Year will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Time category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Month to Year: Step-by-Step Guide
Converting Month to Year involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Month = 0.0833333 yearsExample Calculation:
Convert 60 months: 60 × 0.0833333 = 5 years
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
Need to convert to other time units?
View all Time conversions →What is a Month and a Year?
A month is a unit of time used with calendars, approximately based on the orbital period of the Moon around Earth. The word "month" derives from "Moon" (Proto-Germanic mǣnōth).
Modern Gregorian Calendar Months
In the Gregorian calendar (standard worldwide since 1582), months have irregular lengths:
| Month | Days | Hours | Weeks (approx) | |-----------|----------|-----------|-------------------| | January | 31 | 744 | 4.43 | | February | 28 (29 leap) | 672 (696 leap) | 4.00 (4.14 leap) | | March | 31 | 744 | 4.43 | | April | 30 | 720 | 4.29 | | May | 31 | 744 | 4.43 | | June | 30 | 720 | 4.29 | | July | 31 | 744 | 4.43 | | August | 31 | 744 | 4.43 | | September | 30 | 720 | 4.29 | | October | 31 | 744 | 4.43 | | November | 30 | 720 | 4.29 | | December | 31 | 744 | 4.43 |
Average Month for Conversions
For mathematical conversions, an average month is defined as:
- 1/12th of a year = 365.25 days ÷ 12 = 30.4375 days (often rounded to 30.44 days)
- 730.5 hours (30.4375 × 24)
- 43,830 minutes (730.5 × 60)
- 2,629,800 seconds (43,830 × 60)
- 4.35 weeks (30.4375 ÷ 7)
Lunar Month vs. Calendar Month
- Synodic month (lunar cycle, new moon to new moon): 29.53 days (29 days, 12 hours, 44 minutes, 3 seconds)
- Sidereal month (Moon's orbit relative to stars): 27.32 days
- Gregorian calendar month: 28-31 days (avg 30.44 days)
- Drift: Calendar months drift ~2 days per month from lunar phases
A year is a unit of time based on the orbital period of Earth around the Sun. The word "year" derives from Old English gēar, Proto-Germanic jǣram, related to "to go" (referring to the Sun's apparent journey through the sky).
Types of Years
Tropical year (solar year):
- 365.2422 days (365 days, 5 hours, 48 minutes, 46 seconds)
- Time between successive vernal equinoxes (spring returns)
- Basis for Gregorian calendar (tracks seasons accurately)
Julian year (scientific standard):
- Exactly 365.25 days = 31,557,600 seconds
- Used in astronomy, physics for consistent conversions
- Averages Julian calendar leap year cycle (3 × 365 + 1 × 366 ÷ 4)
Sidereal year:
- 365.2564 days (365 days, 6 hours, 9 minutes, 10 seconds)
- Time for Earth to complete one orbit relative to fixed stars
- ~20 minutes longer than tropical year due to precession of equinoxes
Calendar year (Gregorian):
- 365 days (common year, 3 out of 4 years)
- 366 days (leap year, every 4 years with exceptions)
- Average: 365.2425 days (97 leap years per 400 years)
Year Conversions (Julian Year = 365.25 days)
| Unit | Value | Calculation | |----------|-----------|-----------------| | Days | 365.25 | Standard definition | | Hours | 8,766 | 365.25 × 24 | | Minutes | 525,960 | 8,766 × 60 | | Seconds | 31,557,600 | 525,960 × 60 | | Weeks | 52.18 | 365.25 ÷ 7 | | Months | 12 | Standard calendar division |
Note: The Month is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Year belongs to the imperial/US customary system.
History of the Month and Year
of the Month
1. Ancient Lunar Origins (Pre-3000 BCE)
The concept of the month originated from observing the lunar cycle—the period from one new moon to the next, approximately 29.53 days (synodic month).
Early lunar calendars:
- Babylonian calendar (c. 2000 BCE): 12 lunar months (~354 days per year), with periodic intercalary (13th) months added every 2-3 years to realign with seasons
- Egyptian calendar (c. 3000 BCE): 12 months of exactly 30 days each (360 days) + 5 epagomenal days = 365 days, detached from lunar cycle
- Hebrew/Jewish calendar (c. 1500 BCE): Lunisolar calendar with 12-13 months (29-30 days each), still used today for religious observances
- Chinese calendar (c. 1600 BCE): Lunisolar calendar with 12-13 months, determining Chinese New Year (late January to mid-February)
Why lunar months? Ancient civilizations without artificial lighting noticed the Moon's dramatic visual changes every ~29.5 days, making it an obvious natural timekeeper.
2. Roman Calendar Evolution (753 BCE - 46 BCE)
The Roman calendar underwent dramatic transformations:
Romulus Calendar (753 BCE - legendary):
- 10 months, 304 days total, starting in March (spring equinox)
- Months: Martius (31), Aprilis (30), Maius (31), Junius (30), Quintilis (31), Sextilis (30), September (30), October (31), November (30), December (30)
- Winter gap (~61 days) was unnamed, creating calendar chaos
Numa Pompilius Reform (c. 713 BCE):
- Added January and February to fill winter gap
- 12 months, 355 days total (still 10.25 days short of solar year)
- Required periodic intercalary months (Mercedonius) to realign with seasons
- Romans disliked even numbers, so most months had 29 or 31 days (February got unlucky 28)
Late Roman Republic (c. 100 BCE):
- Calendar administration corrupt—priests (pontifices) manipulated intercalary months for political gain (extending terms, delaying elections)
- Calendar drifted months out of sync with seasons (harvest festivals in wrong seasons)
3. Julian Calendar (46 BCE - 1582 CE)
Julius Caesar's reform (46 BCE):
- Consulted Egyptian astronomer Sosigenes of Alexandria
- Adopted solar year = 365.25 days (365 days + leap day every 4 years)
- Redesigned month lengths to solar-based 28-31 days:
- 31 days: January, March, May, July (Quintilis), September, November
- 30 days: April, June, August (Sextilis), October, December
- 28/29 days: February (unlucky month, kept short)
- 46 BCE = "Year of Confusion" (445 days long to realign calendar with seasons)
Later adjustments:
- 44 BCE: Quintilis renamed July (Julius Caesar, after his assassination)
- 8 BCE: Sextilis renamed August (Augustus Caesar)
- August given 31 days (stealing 1 from February) to match July's prestige, redistributing others
- Final pattern: Jan(31), Feb(28/29), Mar(31), Apr(30), May(31), Jun(30), Jul(31), Aug(31), Sep(30), Oct(31), Nov(30), Dec(31)
Problem with Julian calendar: Solar year = 365.2422 days (not exactly 365.25), so calendar gained ~11 minutes per year = 3 days every 400 years
4. Gregorian Calendar (1582 CE - Present)
Pope Gregory XIII's reform (1582):
- Corrected drift: Removed 10 days (October 4, 1582 → October 15, 1582) to realign with seasons
- New leap year rule:
- Leap year every 4 years (like Julian)
- EXCEPT century years (1700, 1800, 1900) NOT leap years
- EXCEPT century years divisible by 400 (1600, 2000, 2400) ARE leap years
- Result: 97 leap years per 400 years = 365.2425 days average (only 27 seconds/year error)
- Month lengths unchanged from final Julian pattern
Adoption:
- Catholic countries (Spain, Portugal, Italy): Immediately (1582)
- Protestant countries (Britain, colonies): 1752 (removed 11 days: Sept 2 → Sept 14)
- Russia: 1918 (removed 13 days, after October Revolution became November Revolution)
- China: 1912 (Republic of China adoption)
- Turkey: 1926 (secular reforms)
- Now universal for civil purposes worldwide
5. Lunar Calendars Continue
Despite Gregorian dominance, lunar/lunisolar calendars continue for religious/cultural purposes:
- Islamic Hijri calendar: 12 lunar months (354-355 days), cycles through seasons every 33 years, determines Ramadan
- Hebrew calendar: Lunisolar with 12-13 months, determines Jewish holidays
- Chinese calendar: Lunisolar, determines Chinese New Year, Mid-Autumn Festival
- Hindu calendars: Multiple regional lunisolar systems
- Buddhist calendars: Various lunisolar systems across Thailand, Sri Lanka, Myanmar
of the Year
1. Ancient Solar Observation (Pre-3000 BCE)
The concept of the year originated from observing seasonal cycles—the return of spring, flooding seasons, astronomical events (solstices, equinoxes).
Key observations:
- Vernal equinox (spring): Day and night equal length (~March 20)
- Summer solstice: Longest day (~June 21)
- Autumnal equinox (fall): Day and night equal (~September 22)
- Winter solstice: Shortest day (~December 21)
- Tropical year: Time between successive vernal equinoxes = 365.24 days
Why critical? Agricultural societies needed to predict:
- Planting seasons (spring planting window)
- Flooding cycles (Nile River flooded annually June-September)
- Harvest times (fall harvest before winter)
- Animal migration patterns
2. Early Calendar Systems (3000-1000 BCE)
Egyptian Calendar (c. 3000 BCE):
- 365 days = 12 months × 30 days + 5 epagomenal days
- No leap years = drifted ~1 day every 4 years = full cycle every 1,460 years (Sothic cycle)
- Divided into 3 seasons: Inundation (Akhet), Growth (Peret), Harvest (Shemu)
- Problem: Calendar drifted from actual seasons (harvest festivals gradually moved through calendar)
Babylonian Calendar (c. 2000 BCE):
- Lunisolar: 12 lunar months (~354 days) + intercalary 13th month every 2-3 years
- Metonic cycle (discovered ~432 BCE): 19 solar years ≈ 235 lunar months (7 intercalary months in 19 years)
- Better seasonal alignment than pure lunar or 365-day solar calendar
Chinese Calendar (c. 1600 BCE):
- Lunisolar: 12-13 months per year, intercalary months added algorithmically
- Still used today for Chinese New Year (late January to mid-February)
Mesoamerican Calendars (c. 1000 BCE):
- Haab (Maya civil calendar): 365 days = 18 months × 20 days + 5 unlucky days (Wayeb)
- Tzolk'in (ritual calendar): 260 days = 13 numbers × 20 day names
- Calendar Round: 52 Haab years = 73 Tzolk'in cycles (18,980 days)
3. Roman Calendar Evolution (753 BCE - 46 BCE)
Romulus Calendar (753 BCE - legendary):
- 10 months, 304 days, starting in March (spring equinox)
- Winter gap (~61 days) unnamed = calendar chaos
Numa Pompilius Reform (c. 713 BCE):
- Added January and February = 12 months, 355 days
- Required intercalary month (Mercedonius) inserted periodically = political corruption
- Calendar drifted severely (festivals months off from intended seasons)
Problem by 46 BCE: Calendar drifted ~3 months ahead of seasons (spring equinox in mid-summer)
4. Julian Calendar (46 BCE - 1582 CE)
Julius Caesar's reform (46 BCE):
- Consulted Egyptian astronomer Sosigenes of Alexandria
- 365.25-day year: 365 days + leap day every 4 years (February 29)
- 46 BCE = "Year of Confusion" (445 days long) to realign calendar with seasons
- January 1 established as New Year (previously March 1)
Julian leap year rule:
- Every year divisible by 4 = leap year (e.g., 4, 8, 12, ... 2020, 2024)
- Simple, systematic = dramatic improvement over irregular Roman intercalation
Problem with Julian calendar:
- Tropical year = 365.2422 days (not exactly 365.25)
- Julian calendar gains ~11 minutes per year = 3 days every 400 years
- By 1582 CE: Calendar drifted 10 days ahead (vernal equinox on March 11 instead of March 21)
5. Gregorian Calendar (1582 CE - Present)
Pope Gregory XIII's reform (1582):
- Goal: Restore vernal equinox to March 21 (for Easter calculation)
- Correction: Removed 10 days (October 4, 1582 → October 15, 1582)
- New leap year rule:
- Year divisible by 4 = leap year (like Julian)
- EXCEPT century years (1700, 1800, 1900, 2100) = NOT leap year
- EXCEPT century years divisible by 400 (1600, 2000, 2400) = leap year
- Result: 97 leap years per 400 years = 365.2425 days average
- Accuracy: Only 27 seconds/year error = 1 day off every ~3,030 years
Why the reform?
- Easter calculation: Christian Easter tied to vernal equinox (first Sunday after first full moon after March 21)
- Julian drift moved equinox to March 11 = Easter dates increasingly inaccurate
- Catholic Church needed calendar reform for liturgical calendar
Global adoption:
- Catholic countries (Spain, Portugal, Italy, Poland): Immediately (October 1582)
- Protestant countries: Resisted initially (religious conflict with Catholic Pope)
- Britain and colonies: 1752 (removed 11 days: Sept 2 → Sept 14)
- Germany (Protestant states): 1700 (removed 10 days)
- Eastern Orthodox: 1900s (Russia 1918, Greece 1923)
- Non-Christian countries: 20th century for civil purposes
- Japan: 1873 (Meiji era modernization)
- China: 1912 (Republic of China)
- Turkey: 1926 (Atatürk's secular reforms)
- Now universal for international business, diplomacy, science
6. Modern Refinements and Proposals
Leap second (introduced 1972):
- Earth's rotation gradually slowing (tidal friction from Moon)
- Atomic clocks (SI second) vs. Earth's rotation = gradual drift
- Leap second occasionally added (usually June 30 or December 31) to keep atomic time within 0.9 seconds of Earth rotation
- 27 leap seconds added 1972-2016 (~1 per 1.5 years average)
Failed calendar reform proposals:
- World Calendar (1930s-1960s): 4 identical quarters, perpetual calendar (same dates always same day of week), extra "worldsday" outside week
- International Fixed Calendar (early 1900s): 13 months × 28 days + 1 extra day (year day)
- Opposition: Religious groups (Sabbath observance), businesses (calendar change costs), cultural inertia
Why Gregorian calendar persists despite imperfections:
- Universal adoption = massive switching cost
- "Good enough": 1-day error every 3,030 years = negligible for practical purposes
- Cultural entrenchment: Decades, centuries, millennia aligned with current system
Common Uses and Applications: months vs years
Explore the typical applications for both Month (imperial/US) and Year (imperial/US) to understand their common contexts.
Common Uses for months
and Applications
1. Financial Planning and Budgeting
Monthly budget framework:
- Income: Track monthly take-home pay (after taxes)
- Fixed expenses: Rent/mortgage, car payment, insurance (consistent monthly amounts)
- Variable expenses: Groceries, utilities, entertainment (varies month-to-month)
- Savings goals: "Save $500/month" = $6,000/year
- Debt repayment: "Extra $200/month toward credit card" = $2,400/year payoff
Monthly vs. annual thinking:
- $150/month subscription = $1,800/year (psychological impact: monthly feels smaller)
- "Latte factor": $5 daily coffee = $150/month = $1,800/year = $18,000/decade
Monthly financial ratios:
- Rent rule: Rent should be ≤30% of monthly gross income
- 50/30/20 rule: 50% needs, 30% wants, 20% savings (monthly breakdown)
2. Subscription and Membership Economy
Monthly Recurring Revenue (MRR) = business model foundation:
- SaaS (Software as a Service): Monthly subscription pricing (e.g., Adobe Creative Cloud $54.99/month)
- Streaming services: Netflix, Spotify, Disney+ (monthly billing standard)
- Gym memberships: Monthly dues (e.g., $30-100/month depending on gym)
- Amazon Prime: $14.99/month (or $139/year = $11.58/month, annual cheaper)
Monthly vs. annual pricing psychology:
- Annual = higher upfront cost, lower monthly rate, customer lock-in
- Monthly = lower barrier to entry, higher churn risk, higher effective rate
3. Project Management and Milestones
Standard project durations:
- 1-month sprint: Agile/Scrum often uses 2-4 week sprints (close to 1 month)
- 3-month project: Standard short-term project (1 quarter)
- 6-month project: Medium-term initiative (2 quarters, half-year)
- 12-month project: Long-term strategic initiative (full year)
Monthly milestones:
- Month 1: Planning and setup
- Month 2: Development/implementation
- Month 3: Testing and refinement
- Month 4: Launch and monitoring
4. Employment and Compensation
Pay period variations:
- Monthly (12 pay periods/year): Common internationally, especially Europe/Asia
- Pros: Aligns with monthly bills, simpler accounting
- Cons: Long gap between paychecks (especially if month has 31 days)
- Semi-monthly (24 pay periods/year): 1st and 15th of each month
- Pros: More frequent pay (twice per month), aligns with mid-month expenses
- Cons: Pay dates vary (weekends/holidays), inconsistent days between paychecks
- Bi-weekly (26 pay periods/year): Every 2 weeks (e.g., every other Friday)
- Pros: Consistent day of week, 2 "extra" paychecks per year
- Cons: Doesn't align with monthly bills, some months have 3 paychecks
Monthly salary vs. hourly:
- Salaried: Annual salary ÷ 12 = monthly salary (e.g., $72,000/year = $6,000/month)
- Hourly: (Hourly rate × hours/week × 52 weeks) ÷ 12 months (e.g., $25/hr × 40hrs × 52 ÷ 12 = $4,333/month)
5. Calendar Organization
Month as primary calendar unit:
- Monthly view: Standard calendar layout (7 columns × 4-6 rows = 28-42 cells)
- Month numbering: January = 1, February = 2, ... December = 12
- Date notation:
- US: MM/DD/YYYY (month first)
- International (ISO 8601): YYYY-MM-DD (year-month-day)
- European: DD/MM/YYYY (day first)
Month-based planning:
- Goals: "Read 2 books per month" = 24 books/year
- Habits: "Exercise 3 times per week" = 12-13 times per month
- Reviews: "Monthly review" of goals, finances, habits
6. Seasonal Business Cycles
Retail calendar:
- January: Post-holiday sales, fitness equipment (New Year's resolutions)
- February: Valentine's Day
- March-April: Spring cleaning, Easter, tax season
- May: Mother's Day, Memorial Day (unofficial summer start)
- June: Father's Day, graduations, weddings
- July-August: Summer travel, back-to-school shopping (late August)
- September: Labor Day, fall season begins
- October: Halloween
- November: Thanksgiving, Black Friday (biggest shopping day)
- December: Holiday shopping season (Christmas/Hanukkah)
Quarterly thinking (3-month periods):
- Q1 (Jan-Mar): New Year momentum, tax season
- Q2 (Apr-Jun): Spring/early summer, end of fiscal year for many companies
- Q3 (Jul-Sep): Summer slowdown, back-to-school
- Q4 (Oct-Dec): Holiday season, year-end push, budget planning
7. Age and Developmental Milestones
Infant/child development:
- 0-12 months: Tracked monthly (dramatic changes each month)
- 3 months: Lifts head, smiles
- 6 months: Sits up, starts solid foods
- 9 months: Crawls, says "mama/dada"
- 12 months: Walks, first words
- 12-24 months: Often still tracked monthly ("18 months old" vs. "1.5 years")
- 2+ years: Typically switch to years ("3 years old")
Age expression:
- Months (0-23 months): More precise for developmental tracking
- Years (2+ years): Standard for most purposes
- Decades (30s, 40s, etc.): Rough life stages
When to Use years
and Applications
1. Age Calculation
Formula: Current year - Birth year = Age (approximate, adjust if birthday hasn't occurred yet)
Example 1: Born 1990, current year 2025
- Age = 2025 - 1990 = 35 years old (if birthday already passed)
- Age = 34 years old (if birthday hasn't occurred yet this year)
Precise age calculation:
- Born: March 15, 1990
- Today: January 10, 2025
- Age = 2025 - 1990 - 1 = 34 years old (birthday hasn't passed yet, subtract 1)
Century calculation:
- Born 1999: "90s kid" or "90s baby"
- Born 2000-2009: "2000s kid"
- Born 2010+: "2010s kid" or Gen Alpha
2. Interest and Investment Calculations
Simple interest (annual):
- Formula: Interest = Principal × Rate × Time
- Example: $10,000 at 5% APR for 3 years
- Interest = $10,000 × 0.05 × 3 = $1,500
- Total = $10,000 + $1,500 = $11,500
Compound interest (annual compounding):
- Formula: Future Value = Principal × (1 + Rate)^Years
- Example: $10,000 at 5% APY for 3 years
- FV = $10,000 × (1.05)³ = $10,000 × 1.157625 = $11,576.25
Rule of 72 (doubling time):
- Formula: Years to double ≈ 72 ÷ Interest Rate
- Example: 8% annual return → 72 ÷ 8 = 9 years to double
- $10,000 at 8% → $20,000 in 9 years
3. Depreciation (Asset Value Decline)
Straight-line depreciation:
- Formula: Annual Depreciation = (Cost - Salvage Value) ÷ Useful Life Years
- Example: $30,000 car, $5,000 salvage, 5-year life
- Annual depreciation = ($30,000 - $5,000) ÷ 5 = $5,000/year
- Year 1: $30,000 - $5,000 = $25,000
- Year 2: $25,000 - $5,000 = $20,000
Accelerated depreciation:
- Cars typically lose 20-30% value first year, then 15-20% annually
- Electronics: Often lose 30-50% value first year
4. Project and Timeline Planning
Standard project durations:
- 1-year project: Long-term strategic initiative
- Multi-year projects: Infrastructure (3-10 years), construction (2-5 years), software development (1-3 years)
Gantt charts and timelines:
- Years as major milestones
- Year 1: Planning and design
- Year 2: Development and construction
- Year 3: Testing and deployment
- Year 4: Operations and maintenance
5. Insurance and Contracts
Insurance terms:
- Term life insurance: 10-year, 20-year, 30-year terms
- Premiums locked for term duration
- Coverage expires at end of term unless renewed
- Auto insurance: 6-month or 1-year policies (renewed annually/semi-annually)
- Health insurance: 1-year open enrollment period (select plan for following year)
Employment contracts:
- 1-year contract: Fixed-term employment (common for contractors, academics)
- Multi-year contracts: Athletes (3-5 year contracts), executives (2-4 years)
- Non-compete clauses: Often 1-2 years after leaving company
Leases:
- Apartment leases: 1-year standard (12 months)
- Commercial leases: 3-10 years typical
- Car leases: 2-4 years (24-48 months)
6. Statistical and Data Analysis
Time series data:
- Annual data points: GDP growth rate (year-over-year), population (annual census estimates)
- Trend analysis: "5-year moving average" smooths short-term fluctuations
Year-over-year (YoY) comparisons:
- Formula: YoY Growth = (This Year - Last Year) ÷ Last Year × 100%
- Example: Revenue $10M (2023) → $12M (2024)
- YoY growth = ($12M - $10M) ÷ $10M × 100% = 20% YoY growth
Compound Annual Growth Rate (CAGR):
- Formula: CAGR = (Ending Value ÷ Beginning Value)^(1/Years) - 1
- Example: Revenue $10M (2020) → $15M (2025) = 5 years
- CAGR = ($15M ÷ $10M)^(1/5) - 1 = 1.5^0.2 - 1 = 0.0845 = 8.45% CAGR
7. Warranty and Guarantee Periods
Product warranties:
- Electronics: 1-year manufacturer warranty (e.g., Apple 1-year limited warranty)
- Appliances: 1-2 years parts and labor
- Cars: 3-year/36,000-mile bumper-to-bumper, 5-year/60,000-mile powertrain
- Home construction: 1-year builder warranty (workmanship), 10-year structural
Service guarantees:
- Software licenses: 1-year subscription (renewable)
- Extended warranties: 2-5 years beyond manufacturer warranty
Additional Unit Information
About Month (mo)
1. How many days are in a month?
It varies by month:
- 31 days: January, March, May, July, August, October, December (7 months)
- 30 days: April, June, September, November (4 months)
- 28 days: February (non-leap year)
- 29 days: February (leap year, every 4 years with exceptions)
Average month = 30.44 days (365.25 ÷ 12), used for conversions.
Mnemonic: "30 days hath September, April, June, and November. All the rest have 31, except February alone, which has 28 days clear, and 29 in each leap year."
Knuckle trick: Make fists and count across knuckles (31 days) and valleys (30 days, except February).
2. Why do months have different lengths?
Historical reasons:
- Roman calendar origins: 10-month calendar (Romulus) had 304 days, leaving ~61-day winter gap
- Numa Pompilius added January and February (c. 713 BCE), creating 12 months with 355 days
- Julius Caesar (46 BCE): Julian calendar with 365.25-day year required distributing days across 12 months
- Political decisions: July (Julius Caesar) and August (Augustus Caesar) both given 31 days for prestige, shortening February to 28 days
Result: Irregular pattern (31-28-31-30-31-30-31-31-30-31-30-31) due to Roman politics, not astronomy.
3. What is an average month length used for conversions?
Average month = 30.4375 days (often rounded to 30.44 days)
Calculation: 365.25 days per year ÷ 12 months = 30.4375 days per month
- 365.25 accounts for leap year (365 × 3 years + 366 × 1 year = 1,461 days ÷ 4 years = 365.25)
When to use average month:
- Converting months to days/weeks/hours when specific month unknown
- Financial calculations (monthly interest rates, annual salary ÷ 12)
- Age approximations ("6 months old" ≈ 183 days)
When NOT to use average: Specific date calculations (use actual month lengths).
4. Is a month based on the Moon?
Historically, yes. Currently, only approximately.
Etymology: "Month" derives from "Moon" (Old English mōnað, Proto-Germanic mǣnōth).
Lunar cycle: 29.53 days (synodic month, new moon to new moon)
Gregorian calendar month: 28-31 days (avg 30.44 days)
- Drift: Calendar months drift ~2 days per month from lunar phases
- Example: Full moon on January 15 → next full moon ~February 13 (29.5 days later), not February 15
Modern lunar calendars:
- Islamic calendar: Strictly lunar (12 months × 29.5 days = 354 days), cycles through seasons every 33 years
- Hebrew/Chinese calendars: Lunisolar (12-13 months, adding extra month every 2-3 years to stay aligned with seasons)
Why detached? Solar year (365.24 days) and lunar year (354.37 days) are incompatible—12 lunar months = 10.87 days short of solar year.
5. How many weeks are in a month?
Average month = 4.35 weeks (30.44 days ÷ 7 days/week)
Common mistake: Assuming 1 month = 4 weeks (WRONG—actually 4 weeks = 28 days, most months are 30-31 days)
Specific months:
- 28 days (February, non-leap) = 4.00 weeks
- 29 days (February, leap) = 4.14 weeks
- 30 days (April, June, September, November) = 4.29 weeks
- 31 days (January, March, May, July, August, October, December) = 4.43 weeks
Implications:
- "4 weeks pregnant" ≠ "1 month pregnant" (4 weeks = 28 days, 1 month avg = 30.44 days)
- "Save $100/week" = $435/month (not $400)
6. How many months are in a year?
12 months in all major calendar systems (Gregorian, Julian, Hebrew, Chinese, Hindu).
Why 12 months?
- Lunar approximation: 12 lunar cycles (~354 days) close to solar year (365 days)
- Convenient division: 12 has many factors (1, 2, 3, 4, 6, 12), making quarters (3 months), half-years (6 months) easy
- Historical precedent: Babylonian, Roman calendars used 12 months
Alternative proposals (failed):
- French Republican Calendar (1793-1805): 12 months × 30 days + 5 epagomenal days (abandoned after Napoleon)
- International Fixed Calendar (proposed 1930s): 13 months × 28 days + 1 extra day (never adopted, opposed by religious groups)
7. What is a leap year and how does it affect months?
Leap year: Year with 366 days (not 365), adding 1 extra day to February (29 days instead of 28).
Leap year rule (Gregorian calendar):
- Year divisible by 4 = leap year (e.g., 2024)
- EXCEPT century years (1700, 1800, 1900) = NOT leap year
- EXCEPT century years divisible by 400 (1600, 2000, 2400) = leap year
Why leap years? Solar year = 365.2422 days (not exactly 365), so calendar gains ~0.2422 days per year = ~1 day every 4 years. Adding leap day keeps calendar aligned with seasons.
Impact on months:
- Only February affected (28 → 29 days)
- Leap year: 366 days = 52 weeks + 2 days (52.29 weeks)
- Non-leap year: 365 days = 52 weeks + 1 day (52.14 weeks)
Next leap years: 2024, 2028, 2032, 2036, 2040
8. What is the origin of month names?
Month names (Gregorian calendar, from Latin):
| Month | Origin | Meaning | |-----------|-----------|-------------| | January | Janus (Roman god) | God of beginnings, doorways (two faces looking forward/backward) | | February | Februa (Roman purification festival) | Purification ritual held mid-February | | March | Mars (Roman god) | God of war (originally first month of Roman year) | | April | Aprilis (Latin) | "To open" (buds opening in spring) or Aphrodite (Greek goddess) | | May | Maia (Roman goddess) | Goddess of growth, spring | | June | Juno (Roman goddess) | Goddess of marriage, queen of gods | | July | Julius Caesar | Roman dictator (month of his birth), originally Quintilis ("fifth") | | August | Augustus Caesar | First Roman emperor, originally Sextilis ("sixth") | | September | Septem (Latin) | "Seven" (originally 7th month before January/February added) | | October | Octo (Latin) | "Eight" (originally 8th month) | | November | Novem (Latin) | "Nine" (originally 9th month) | | December | Decem (Latin) | "Ten" (originally 10th month) |
Historical shift: September-December originally matched their numeric names (7th-10th months) when Roman year started in March. Adding January/February shifted them to 9th-12th positions.
9. Why is February the shortest month?
Roman superstition and politics:
- Roman numerology: Romans considered even numbers unlucky, so most months had 29 or 31 days (odd numbers)
- February = unlucky month: Month of purification rituals (Februa), associated with death/underworld, so Romans kept it short
- Julius Caesar's reform (46 BCE): Distributed days to create 365.25-day year, February remained shortest at 28 days
- Augustus's adjustment (8 BCE): Legend says Augustus took 1 day from February (29 → 28) to make August 31 days (matching July), but historians dispute this—likely just continued existing pattern
Result: February = 28 days (29 in leap years), shortest month by 1-3 days.
10. What are the financial quarters?
Financial quarters (Q1, Q2, Q3, Q4): 3-month periods dividing the fiscal year for business reporting.
Calendar year quarters:
- Q1 = January, February, March (90/91 days)
- Q2 = April, May, June (91 days)
- Q3 = July, August, September (92 days)
- Q4 = October, November, December (92 days)
Fiscal year variations: Many companies/governments use different fiscal years:
- US federal government: Oct 1 - Sep 30 (Q1 = Oct-Dec)
- UK government: Apr 1 - Mar 31 (Q1 = Apr-Jun)
- Japan/India: Apr 1 - Mar 31
- Australia: Jul 1 - Jun 30
Why quarters? Balance between frequent reporting (not too infrequent like annual) and manageable workload (not too frequent like monthly for major reporting).
11. How do I calculate age in months?
Formula: (Current year - Birth year) × 12 + (Current month - Birth month)
Example 1: Born March 15, 2020, today is June 15, 2024
- (2024 - 2020) × 12 + (6 - 3) = 4 × 12 + 3 = 51 months old
Example 2: Born November 20, 2022, today is January 10, 2024
- (2024 - 2022) × 12 + (1 - 11) = 2 × 12 - 10 = 14 months old
Precision note: Calculation above assumes same day of month. For exact age:
- If current day ≥ birth day: Use formula above
- If current day < birth day: Subtract 1 month (haven't reached full month yet)
When to use months for age:
- 0-23 months: Infant/toddler development changes rapidly monthly
- 24+ months: Typically switch to years ("2 years old" not "24 months old")
12. What's the difference between bi-monthly and semi-monthly?
Confusing terminology:
Bi-monthly = Ambiguous (avoid using)
- Meaning 1: Every 2 months (6 times per year)
- Meaning 2: Twice per month (24 times per year)
Semi-monthly = Twice per month (24 times per year)
- Example: Paycheck on 1st and 15th of each month
- 12 months × 2 = 24 pay periods per year
Bi-weekly = Every 2 weeks (26 times per year, not 24)
- Example: Paycheck every other Friday
- 52 weeks ÷ 2 = 26 pay periods per year
Recommendation: Avoid "bi-monthly" (ambiguous). Use "every 2 months" (6×/year) or "twice per month"/"semi-monthly" (24×/year).
About Year (yr)
1. How many days are in a year?
It depends on the type of year:
- Common year (Gregorian): 365 days (occurs 3 out of 4 years)
- Leap year (Gregorian): 366 days (occurs every 4 years, with exceptions)
- Julian year (scientific standard): Exactly 365.25 days
- Tropical year (astronomical): 365.2422 days (365 days, 5 hours, 48 minutes, 46 seconds)
- Gregorian average: 365.2425 days (97 leap years per 400 years)
For most conversions: Use 365.25 days (Julian year standard).
2. What is a leap year?
Leap year: Year with 366 days instead of 365, adding February 29 (leap day).
Gregorian leap year rule:
- Year divisible by 4 → leap year (e.g., 2024, 2028)
- EXCEPT century years (1700, 1800, 1900, 2100) → NOT leap year
- EXCEPT century years divisible by 400 (1600, 2000, 2400) → leap year
Why leap years?
- Tropical year = 365.2422 days (not exactly 365)
- Without leap years: Calendar drifts ~1 day every 4 years = 25 days every century
- Leap years keep calendar aligned with seasons
Next leap years: 2024, 2028, 2032, 2036, 2040, 2044, 2048
3. Why is 365.25 days often used for a year in calculations?
365.25 days = Julian year, the scientific standard for conversions and calculations.
Calculation: Average of Julian calendar leap year cycle
- 3 common years (365 days each) + 1 leap year (366 days) = 1,461 days
- 1,461 days ÷ 4 years = 365.25 days/year
Advantages:
- Exact value (no decimals beyond 2 places)
- Simple calculations: Multiply by 365.25 for day conversions
- Scientific standard: Used in astronomy, physics, engineering
- Defined precisely: 1 Julian year = 31,557,600 seconds exactly
When to use 365.25: General conversions, scientific calculations, multi-year projections.
When NOT to use: Specific date calculations (use actual calendar with leap years).
4. How many seconds are in a year?
Julian year (365.25 days):
- 1 year = 365.25 days × 24 hours/day × 60 minutes/hour × 60 seconds/minute
- 1 year = 365.25 × 86,400 seconds/day
- 1 year = 31,557,600 seconds exactly
Tropical year (365.2422 days):
- 365.2422 × 86,400 = 31,556,925.2 seconds (astronomical year)
Common year (365 days):
- 365 × 86,400 = 31,536,000 seconds
Leap year (366 days):
- 366 × 86,400 = 31,622,400 seconds
Standard answer: 31,557,600 seconds (Julian year).
5. What is the difference between calendar year and fiscal year?
Calendar year:
- January 1 - December 31
- Standard Gregorian calendar year
- Used for personal taxes (US), general dating, most non-business contexts
Fiscal year (FY):
- Any 12-month accounting period chosen by organization for financial reporting
- Often NOT January-December
- Allows companies to align reporting with business cycles
Common fiscal years:
- US federal government: October 1 - September 30 (FY2025 = Oct 2024-Sep 2025)
- UK government: April 1 - March 31
- Retailers: Often end January 31 (includes holiday season)
- Universities: Often July 1 - June 30 (aligns with academic year)
Why different fiscal years?
- Seasonal businesses: Retailers want holiday sales (Nov-Dec) mid-year, not at year-end (accounting complexity)
- Budgeting cycles: Governments approve budgets before fiscal year starts
- Tax planning: Align fiscal year with tax advantages
6. How old am I in years?
Simple formula: Current year - Birth year (adjust if birthday hasn't passed)
Precise calculation:
- Subtract birth year from current year
- If current date < birthday this year, subtract 1
Example 1:
- Born: June 15, 1995
- Today: October 20, 2025
- Age = 2025 - 1995 = 30 (birthday already passed in 2025) → 30 years old
Example 2:
- Born: November 10, 1995
- Today: October 20, 2025
- Age = 2025 - 1995 - 1 = 29 (birthday hasn't passed yet in 2025) → 29 years old
Programming formula:
age = current_year - birth_year
if (current_month < birth_month) OR (current_month == birth_month AND current_day < birth_day):
age = age - 1
7. What is the tropical year vs. sidereal year?
Tropical year (solar year):
- 365.2422 days (365 days, 5 hours, 48 minutes, 46 seconds)
- Time between successive vernal equinoxes (spring returns)
- Basis for Gregorian calendar (tracks seasons)
- What we use for civil calendar
Sidereal year:
- 365.2564 days (365 days, 6 hours, 9 minutes, 10 seconds)
- Time for Earth to complete one orbit relative to fixed stars
- ~20 minutes (~0.014 days) longer than tropical year
Why the difference?
- Precession of equinoxes: Earth's rotational axis wobbles (like spinning top)
- Axis completes full wobble every ~25,800 years (Platonic year)
- Vernal equinox drifts westward ~50 arcseconds per year relative to stars
- Result: Tropical year (season-based) slightly shorter than sidereal year (star-based)
Which to use?
- Tropical year: Calendar purposes (Gregorian calendar tracks seasons)
- Sidereal year: Astronomy (tracking Earth's orbit relative to stars)
8. Why did the Gregorian calendar replace the Julian calendar?
Problem with Julian calendar:
- Julian year = 365.25 days (365 days + leap day every 4 years)
- Tropical year = 365.2422 days
- Difference: 365.25 - 365.2422 = 0.0078 days/year = ~11 minutes/year
- Drift: 3 days every 400 years
Impact by 1582:
- Calendar drifted 10 days ahead of seasons (1,257 years × 11 min/year ≈ 10 days)
- Vernal equinox on March 11 instead of March 21
- Easter calculation increasingly inaccurate (tied to vernal equinox)
Gregorian solution:
- Removed 10 days immediately (Oct 4, 1582 → Oct 15, 1582)
- New leap year rule: Skip 3 leap years every 400 years (century years not divisible by 400)
- Result: 365.2425 days/year average (97 leap years per 400 years)
- Error: Only 27 seconds/year = 1 day off every ~3,030 years
Success: Gregorian calendar now universal for civil purposes worldwide.
9. What are decade, century, and millennium?
Decade:
- 10 years
- Examples: 1990s (1990-1999), 2020s (2020-2029)
- Casual usage: Often refers to cultural/generational period
Century:
- 100 years
- 20th century = 1901-2000 (NOT 1900-1999, because no year 0)
- 21st century = 2001-2100 (NOT 2000-2099)
- Notation: "19th century" or "1800s" (informal)
Millennium:
- 1,000 years
- 1st millennium = 1-1000 CE
- 2nd millennium = 1001-2000 CE
- 3rd millennium = 2001-3000 CE
- Y2K (Year 2000) celebrated new millennium, but technically started 2001
Why century/millennium boundaries confusing?
- No year 0 in Gregorian calendar (1 BCE → 1 CE)
- 1st century = years 1-100 (not 0-99)
- Centuries numbered one ahead of their "hundreds digit" (1900s = 20th century)
10. How many hours/minutes are in a year?
Julian year (365.25 days):
- Hours: 365.25 days × 24 hours/day = 8,766 hours
- Minutes: 8,766 hours × 60 minutes/hour = 525,960 minutes
- Seconds: 525,960 minutes × 60 seconds/minute = 31,557,600 seconds
Common year (365 days):
- Hours: 365 × 24 = 8,760 hours
- Minutes: 8,760 × 60 = 525,600 minutes (famous from musical "Rent": "525,600 minutes, how do you measure a year?")
Leap year (366 days):
- Hours: 366 × 24 = 8,784 hours
- Minutes: 8,784 × 60 = 527,040 minutes
Standard answer: 8,766 hours or 525,960 minutes (Julian year).
11. What is a leap second?
Leap second: Extra second occasionally added to Coordinated Universal Time (UTC) to keep atomic time synchronized with Earth's rotation.
Why needed?
- Atomic clocks (SI second): Extremely precise, constant
- Earth's rotation: Gradually slowing (tidal friction from Moon ~2 milliseconds per century)
- Drift: Atomic time gradually diverges from Earth's actual rotation
- Solution: Add leap second when difference approaches 0.9 seconds
Implementation:
- Usually added June 30 or December 31
- Clock reads: 23:59:59 → 23:59:60 → 00:00:00 (extra second)
- 27 leap seconds added 1972-2016 (~1 every 1.5 years)
- No leap seconds 2017-present (Earth's rotation hasn't required it)
Controversy:
- Causes computer system problems (software doesn't expect 60-second minutes)
- Proposed abolition: Let atomic time and Earth rotation drift, adjust in larger increments decades later
12. How do I convert years to other units?
Quick conversion formulas (Julian year = 365.25 days):
Years to days:
- days = years × 365.25
- Example: 3 years = 3 × 365.25 = 1,095.75 days
Years to weeks:
- weeks = years × 52.18 (365.25 ÷ 7)
- Example: 2 years = 2 × 52.18 = 104.36 weeks
Years to months:
- months = years × 12
- Example: 5 years = 5 × 12 = 60 months
Years to hours:
- hours = years × 8,766 (365.25 × 24)
- Example: 1 year = 8,766 hours
Years to seconds:
- seconds = years × 31,557,600 (365.25 × 86,400)
- Example: 1 year = 31,557,600 seconds
Years to decades/centuries:
- decades = years ÷ 10
- centuries = years ÷ 100
Conversion Table: Month to Year
| Month (mo) | Year (yr) |
|---|---|
| 0.5 | 0.042 |
| 1 | 0.083 |
| 1.5 | 0.125 |
| 2 | 0.167 |
| 5 | 0.417 |
| 10 | 0.833 |
| 25 | 2.083 |
| 50 | 4.167 |
| 100 | 8.333 |
| 250 | 20.833 |
| 500 | 41.667 |
| 1,000 | 83.333 |
People Also Ask
How do I convert Month to Year?
To convert Month to Year, enter the value in Month in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our time converter page to convert between other units in this category.
Learn more →What is the conversion factor from Month to Year?
The conversion factor depends on the specific relationship between Month and Year. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Year back to Month?
Yes! You can easily convert Year back to Month by using the swap button (⇌) in the calculator above, or by visiting our Year to Month converter page. You can also explore other time conversions on our category page.
Learn more →What are common uses for Month and Year?
Month and Year are both standard units used in time measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our time converter for more conversion options.
For more time conversion questions, visit our FAQ page or explore our conversion guides.
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Other Time Units and Conversions
Explore other time units and their conversion options:
- Second (s) • Month to Second
- Minute (min) • Month to Minute
- Hour (h) • Month to Hour
- Day (d) • Month to Day
- Week (wk) • Month to Week
- Millisecond (ms) • Month to Millisecond
- Microsecond (μs) • Month to Microsecond
- Nanosecond (ns) • Month to Nanosecond
- Decade (dec) • Month to Decade
- Century (c) • Month to Century
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official time standards and definitions
Bureau International des Poids et Mesures — Definition of the SI base unit for time
Last verified: December 3, 2025