Year to Century Converter
Convert years to centuries with our free online time converter.
Quick Answer
1 Year = 0.01 centuries
Formula: Year × conversion factor = Century
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.
Year to Century Calculator
How to Use the Year to Century Calculator:
- Enter the value you want to convert in the 'From' field (Year).
- The converted value in Century 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 Year to Century: Step-by-Step Guide
Converting Year to Century involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Year = 0.01 centuriesExample Calculation:
Convert 60 years: 60 × 0.01 = 0.6 centuries
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 Year and a Century?
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 |
A century is a unit of time equal to 100 consecutive years. The word derives from Latin "centum" (one hundred).
Duration in Other Units
1 century equals:
- 100 years (exactly)
- 10 decades (100 ÷ 10)
- 1,200 months (100 × 12)
- ~5,217 weeks (100 × 52.17)
- 36,524 days (100 common years) or 36,525 days (accounting for ~25 leap years)
- Average: 36,525 days (100 × 365.25)
- 876,600 hours (36,525 × 24)
- 52,596,000 minutes (876,600 × 60)
- 3,155,760,000 seconds (52,596,000 × 60)
Century Boundaries: The 1 vs. 0 Debate
Formal reckoning (technically correct):
- 1st century: 1-100 CE
- 18th century: 1701-1800
- 19th century: 1801-1900
- 20th century: 1901-2000
- 21st century: 2001-2100
Why? Because there was no year 0 in the Gregorian calendar (1 BCE → 1 CE directly), the first century was years 1-100, not 0-99.
Popular usage (dominant in practice):
- 18th century: "The 1700s" (1700-1799)
- 19th century: "The 1800s" (1800-1899)
- 20th century: "The 1900s" (1900-1999)
- 21st century: "The 2000s onward" (2000-2099)
Reality: Popular usage dominates. When people say "20th century," they typically mean 1900-1999, not 1901-2000. The millennium celebration happened January 1, 2000, not January 1, 2001, despite formal correctness.
Note: The Year is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Century belongs to the imperial/US customary system.
History of the Year and Century
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
of the Century Concept
1. Ancient Origins: Roman Centuria (509 BCE - 27 BCE)
Roman military organization:
- Centuria (plural: centuriae) = Roman military unit of approximately 100 soldiers (later reduced to 80)
- Led by a centurion (centurio)
- Latin "centum" = one hundred
- 6 centuries = 1 cohort; 10 cohorts = 1 legion (~6,000 soldiers)
Early timekeeping:
- Romans used Ab urbe condita (AUC, "from the founding of the city") dating from Rome's legendary founding (753 BCE)
- No systematic use of "century" for 100-year periods yet
- Time organized by consulships, reigns, dynasties
2. Calendar Development and Anno Domini Dating (1 CE - 1582 CE)
Anno Domini (AD) system:
- Dionysius Exiguus (c. 525 CE): Calculated years from Jesus Christ's birth
- Introduced Anno Domini (AD, "in the year of the Lord") dating
- Critical error: No year 0 (went directly from 1 BCE to 1 CE)
- This creates century boundary confusion still debated today
Julian Calendar (46 BCE - 1582 CE):
- Julius Caesar introduced 365.25-day year (leap year every 4 years)
- Provided stable framework for long-term chronology
- Enabled systematic dating of events over centuries
Gregorian Calendar Reform (1582 CE):
- Pope Gregory XIII corrected Julian calendar drift
- Established modern calendar system still used today
- Removed 10 days (October 4, 1582 → October 15, 1582)
- Century years divisible by 400 are leap years (1600, 2000), others not (1700, 1800, 1900)
3. Renaissance and Enlightenment: Historical Periodization (1400s-1700s)
Systematic historiography emerged:
- 15th-16th centuries: Renaissance scholars developed historical chronologies
- 17th-18th centuries: Enlightenment historians systematized century-based periodization
- Edward Gibbon (Decline and Fall of the Roman Empire, 1776-1789): Used century-scale analysis
Why centuries became standard:
- Generational scale: ~4 generations per century = intergenerational change visible but comprehensible
- Administrative records: Tax records, census data, government documents accumulated over centuries
- Pattern recognition: 100-year scale reveals structural changes invisible in decade-scale analysis
- Round number psychology: Base-10 counting makes 100-year periods psychologically satisfying
Periodization labels emerged:
- "The 16th century" = 1500s Renaissance, Reformation
- "The 17th century" = 1600s Scientific Revolution, Baroque
- "The 18th century" = 1700s Age of Enlightenment, Industrial Revolution begins
4. 19th Century: Century as Historical Framework (1801-1900)
The "long 19th century" concept:
- Historians sometimes define as 1789-1914 (French Revolution to WWI)
- Captures coherent historical era despite not matching formal century boundaries
Major 19th-century transformations:
- Industrial Revolution (1760-1840): Steam power, factories, railroads
- Urbanization: Rural → urban population shift
- Imperialism: European colonial empires peak
- Scientific progress: Darwin, Maxwell, Mendel
- Political revolutions: 1848 Revolutions, unification of Germany/Italy
- Technological: Telegraph, telephone, photography, electricity
Century consciousness:
- People in 1800s increasingly thought in century-scale terms
- "The spirit of the 19th century" = common phrase
- Fin de siècle (end of century, 1890s-1900s) = cultural movement
5. 20th Century: Century of Extremes (1901-2000)
Eric Hobsbawm's "short 20th century" (1914-1991):
- WWI start to Soviet Union collapse
- Captures coherent historical narrative despite formal century boundaries
Major 20th-century transformations:
- World Wars: WWI (1914-1918), WWII (1939-1945)
- Ideological conflict: Fascism, Communism, Capitalism compete
- Cold War (1947-1991): US vs. USSR, nuclear arms race
- Decolonization: European empires disintegrate (1940s-1970s)
- Technological revolutions:
- Automobiles, airplanes (early 1900s)
- Nuclear energy (1940s)
- Computers (1940s-1950s)
- Space exploration (1950s-1960s)
- Internet (1990s)
- Mobile phones (1990s-2000s)
- Population explosion: 1.6 billion (1900) → 6.1 billion (2000)
- Medical advances: Antibiotics, vaccines, life expectancy doubled
- Environmental: Climate change, ozone depletion, biodiversity loss
Century labeling:
- "The American Century" (Henry Luce, 1941): US dominance of 20th century
- "The People's Century" (BBC, 1995): Mass politics, democracy spread
6. 21st Century: Digital Age and Beyond (2001-Present)
Millennium transition debate:
- Popular celebration: January 1, 2000 (Y2K)
- Formal start: January 1, 2001
- Most people celebrated 2000 despite pedantic correctness
21st-century defining features (so far):
- 9/11 attacks (2001): "War on Terror" begins
- Digital revolution: Smartphones ubiquitous (iPhone 2007)
- Social media: Facebook, Twitter, Instagram, TikTok
- Climate crisis: Accelerating global warming, extreme weather
- COVID-19 pandemic (2020-2023): Global disruption
- AI revolution: ChatGPT (2022), generative AI breakthroughs
- Geopolitical shifts: Rise of China, multipolar world
- Economic: 2008 Financial Crisis, wealth inequality
"21st-century skills": Digital literacy, critical thinking, adaptability
Common Uses and Applications: years vs centuries
Explore the typical applications for both Year (imperial/US) and Century (imperial/US) to understand their common contexts.
Common Uses for 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
When to Use centuries
and Applications
1. Historical Analysis and Research
Century-by-century comparison:
- Economic growth: "19th-century industrialization vs. 20th-century information age"
- Warfare evolution: "19th-century muskets → 20th-century machine guns → 21st-century drones"
- Life expectancy trends: Analyzed century-by-century
Academic papers:
- "This study examines voting patterns across two centuries (1800s-1900s)"
- "Century-scale climate reconstructions"
2. Art, Literature, and Cultural Studies
Periodization:
- "18th-century literature": Age of Enlightenment, Voltaire, Swift, Johnson
- "19th-century novel": Dickens, Austen, Tolstoy, Dostoevsky
- "20th-century art": Impressionism, Cubism, Surrealism, Abstract Expressionism
Art history courses: Often organized by century ("Art of the 17th Century")
3. Genealogy and Family History
Tracing ancestry:
- 4-5 generations per century = century scale ideal for family trees
- "My great-great-grandfather lived in the 19th century"
- Immigration records, census data organized by century
Life stages across centuries:
- Born late 1800s, died mid-1900s = lived through two centuries
4. Climate and Environmental Science
Century-scale climate patterns:
- Medieval Warm Period (10th-13th centuries): Warmer than average
- Little Ice Age (14th-19th centuries): Cooler than average
- 20th-21st century warming: Anthropogenic climate change
Projections:
- "By end of 21st century, sea level rise 1-2 meters"
5. Economic and Development Studies
Long-term economic trends:
- 19th century: Agricultural → industrial economies
- 20th century: Industrial → service/information economies
- 21st century: Digital/knowledge economies
Development indicators: Tracked over centuries (literacy, GDP, poverty)
6. Philosophy and Long-Term Thinking
"Think in centuries":
- Long Now Foundation: 10,000-year thinking
- Contrast with short-term thinking (quarterly earnings, election cycles)
Philosophical movements:
- 18th century: Enlightenment rationalism
- 19th century: Romanticism, existentialism emerges
- 20th century: Postmodernism
7. Legal and Property Rights
Land ownership records:
- Property deeds reference century-old transactions
- "Century farms": Farms in same family 100+ years
Copyright:
- Life + 70 years = often extends into next century after author's death
Additional Unit Information
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
About Century (c)
1. How many years are in a century?
Exactly 100 years. The word "century" comes from Latin "centum" (one hundred).
Other units:
- 1 century = 100 years = 10 decades = 1,200 months = ~36,525 days
2. When did the 21st century begin?
Formal answer: January 1, 2001 (because there was no year 0, the 1st century was years 1-100, so the 21st century is 2001-2100).
Popular answer: January 1, 2000 (most people celebrated the new millennium in 2000, and colloquially refer to "the 2000s" as the start of the 21st century).
Reality: Both are used; formal definition is technically correct, but popular usage dominates in practice.
3. Why is the 1800s called the 19th century?
Because of how centuries are numbered:
- 1st century = years 1-100
- 2nd century = years 101-200
- 18th century = years 1701-1800
- 19th century = years 1801-1900 (the "1800s")
- 20th century = years 1901-2000 (the "1900s")
Rule: Century number = (hundreds digit + 1). So 1800s → century 18+1 = 19th century.
4. How many generations are in a century?
Approximately 4-5 generations, assuming ~20-25 years per generation.
Calculation:
- If generation = 25 years → 100 ÷ 25 = 4 generations per century
- If generation = 20 years → 100 ÷ 20 = 5 generations per century
Example: Great-great-grandparents often lived in a different century than you.
5. Is a century a standard unit in science?
No. The century is not part of the International System of Units (SI). The SI base unit for time is the second.
Scientific time units:
- Years (Julian year = 365.25 days exactly)
- Kiloyears (kyr): 1,000 years
- Megayears (Myr): 1,000,000 years
- Gigayears (Gyr): 1,000,000,000 years
Century usage: Common in history, demography, climate science, but not formal SI unit.
6. How many days are in a century?
Approximately 36,525 days (accounting for leap years).
Calculation:
- 100 years × 365 days = 36,500 days
- Plus ~25 leap days per century = 36,525 days total
Exact number varies: Depends on leap year distribution (Gregorian calendar: 97 leap years per 400 years).
7. What is the difference between centennial and bicentennial?
Centennial: 100th anniversary (1 century)
Bicentennial: 200th anniversary (2 centuries)
Other -ennial terms:
- Sesquicentennial: 150th anniversary (1.5 centuries)
- Tercentennial/Tricentennial: 300th anniversary (3 centuries)
- Quadricentennial: 400th anniversary (4 centuries)
- Quincentennial: 500th anniversary (5 centuries)
8. Can a person live in three different centuries?
Yes, but extremely rare.
Requirements:
- Born in one century (e.g., 1898, 19th century)
- Live through next century (1900s, 20th century)
- Live into third century (2000s, 21st century)
- Requires living 102+ years if born in last years of century
Example: Born December 1898 (19th century) → lived through 20th century (1901-2000) → died January 2001 (21st century) = lived in 3 centuries despite being only 102 years old.
9. What is a "long century" in history?
Historical concept: Period longer than 100 years but representing a coherent historical era.
Famous examples:
- "Long 19th century" (1789-1914): French Revolution to WWI start
- "Long 18th century" (1688-1815): Glorious Revolution to Waterloo
- "Short 20th century" (1914-1991): Conversely, WWI to USSR collapse = only 77 years but captures coherent era
Why useful: Historical eras don't align neatly with formal century boundaries; "long/short century" captures thematic unity.
10. How do I calculate how many centuries between two years?
Formula: centuries = (ending year - starting year) ÷ 100
Examples:
- 1500 to 2000: (2000 - 1500) ÷ 100 = 5 centuries (500 years)
- 1776 to 2024: (2024 - 1776) ÷ 100 = 2.48 centuries (~248 years)
- 1900 to 2100: (2100 - 1900) ÷ 100 = 2 centuries (200 years)
11. What is "fin de siècle"?
French phrase: "End of the century" (literally "end of era")
Historical meaning: Cultural period at end of 19th century (1890s-1900s) characterized by:
- Cultural pessimism mixed with optimism
- Decadence, Art Nouveau
- Anxiety about modernity
- Transition into new century
Modern usage: Any "end of century" cultural moment (Y2K was modern "fin de siècle").
12. How many centuries in a millennium?
10 centuries = 1 millennium
Conversions:
- 1 century = 0.1 millennia (100 years)
- 5 centuries = 0.5 millennia (500 years)
- 10 centuries = 1 millennium (1,000 years)
- 20 centuries = 2 millennia (2,000 years)
Conversion Table: Year to Century
| Year (yr) | Century (c) |
|---|---|
| 0.5 | 0.005 |
| 1 | 0.01 |
| 1.5 | 0.015 |
| 2 | 0.02 |
| 5 | 0.05 |
| 10 | 0.1 |
| 25 | 0.25 |
| 50 | 0.5 |
| 100 | 1 |
| 250 | 2.5 |
| 500 | 5 |
| 1,000 | 10 |
People Also Ask
How do I convert Year to Century?
To convert Year to Century, enter the value in Year 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 Year to Century?
The conversion factor depends on the specific relationship between Year and Century. 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 Century back to Year?
Yes! You can easily convert Century back to Year by using the swap button (⇌) in the calculator above, or by visiting our Century to Year converter page. You can also explore other time conversions on our category page.
Learn more →What are common uses for Year and Century?
Year and Century 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.
Helpful Conversion Guides
Learn more about unit conversion with our comprehensive guides:
All Time Conversions
Other Time Units and Conversions
Explore other time units and their conversion options:
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