1
366
days
29
days
2,028
2,020
4
years
6
years
21
years
1
366
days
29
days
2,028
2,020
4
years
6
years
21
years
The Leap Year Calculator determines whether any given year is a leap year, shows how many days are in February that year, finds the next upcoming leap year, and counts leap years within any range. Leap years are a fundamental correction mechanism in the Gregorian calendar that keeps our civil calendar synchronized with Earth's orbit around the Sun.
The Earth takes approximately 365.2422 days (one solar year) to complete one orbit around the Sun. A standard 365-day calendar falls short by about 0.2422 days per year. Without correction, this gap accumulates: after 100 years, the calendar would be off by ~24 days, shifting seasons dramatically — January would eventually feel like spring in the Northern Hemisphere. The solution is to add a 'leap day' (February 29) roughly every 4 years.
However, 365.25 days per year (one leap day every exactly 4 years) overcorrects slightly — the solar year is 365.2422 days, not 365.25. This 0.0078-day annual surplus accumulates to about 3 extra days every 400 years. The Gregorian calendar correction handles this elegantly with a three-part rule:
This rule means 1900 was not a leap year (divisible by 100, not by 400), but 2000 was (divisible by 400). This gives an average year length of exactly 365.2425 days — extremely close to the actual 365.2422, with an error of just 1 day per 3,236 years. Future centuries: 2100, 2200, and 2300 will not be leap years; 2400 will be.
Leap year quirks: people born on February 29 (called 'leaplings' or 'leapers') technically have a birthday only every 4 years. Many celebrate on February 28 or March 1 in non-leap years. The odds of being born on February 29 are approximately 1 in 1,461. Famous February 29 birthdays include composer Gioachino Rossini (1792) and motivational speaker Tony Robbins (1960).
Leap year rule: (year % 4 === 0) AND (year % 100 !== 0 OR year % 400 === 0). This is the complete Gregorian calendar rule. In JavaScript: a simple boolean test. For the leap year range count, the calculator iterates through each year in the range and applies the same rule. Next leap year: increments from current year until the rule is satisfied.
If a year is a leap year, February has 29 days and the year has 366 days total. The next leap year output shows when the next extra day arrives. The range count is useful for calculating day counts over multi-year spans — the number of leap days affects total days significantly over long periods.
Inputs
Results
2024 is a leap year: divisible by 4, not by 100. Next leap year is 2028. Range 2020-2040 has 6 leap years.
Inputs
Results
1900 is NOT a leap year: divisible by 100 but not by 400. This surprises many people who assume every 4th year is a leap year.
A year is a leap year if: (1) it is divisible by 4, AND (2) it is NOT divisible by 100, OR it IS divisible by 400. Examples: 2024 (yes), 2100 (no — divisible by 100 not 400), 2000 (yes — divisible by 400).
The century rule: years divisible by 100 are normally not leap years. But years divisible by 400 are exceptions. 2000 / 400 = 5 exactly, so 2000 is a leap year. 1900 / 400 = 4.75, so 1900 is not. Next non-leap century year: 2100.
Typically every 4 years (2024, 2028, 2032...). However, every 100 years a leap year is skipped (2100, 2200, 2300). Every 400 years the skip is undone (2000, 2400). On average, there are 97 leap years per 400-year cycle.
'Leaplings' or 'leap year babies' celebrate their calendar birthday only when February 29 occurs. In non-leap years, they typically celebrate on either February 28 or March 1 based on personal preference or legal jurisdiction.
No — leap year and daylight saving time are independent systems. DST adds/removes an hour in spring and fall for different reasons (energy savings, daylight optimization). A leap day simply adds 24 hours to the calendar year.
February is the shortest month and was historically the last month of the Roman calendar year (the year started in March in ancient Rome). When the calendar was reformed, the intercalary day was added at the end of the old year — February — and this convention persisted into the Gregorian calendar.
Separate from leap years, a leap second is occasionally added to UTC (atomic time) to account for irregular variations in Earth's rotation. Unlike leap days (predictable by formula), leap seconds are announced only months in advance by the International Earth Rotation Service.
From 2000 to 2096, there are 25 leap years (every 4 years). 2100 is NOT a leap year. So from 2000 to 2100 there are 25 leap years total. Use the range feature of this calculator to verify: enter 2000 and 2100.
Yes — this happens around century years that are not leap years. After 1896, the next leap year was 1904 (8-year gap because 1900 was skipped). The same will happen after 2096, with the next leap year being 2104.
The Julian calendar (introduced by Julius Caesar in 45 BC) used a simpler rule: every year divisible by 4 is a leap year, with no century exception. This accumulated an error of 1 day every 128 years. By 1582, the Julian calendar was 10 days behind the solar year, prompting Pope Gregory XIII to reform it.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
How helpful was this calculator?
Be the first to rate!
Day of Week Calculator
Day of Week & Calendar Calculators
Week Number Calculator
Day of Week & Calendar Calculators
Day of Year Calculator
Day of Week & Calendar Calculators
Calendar Calculator
Day of Week & Calendar Calculators
Moon Phase Calculator
Day of Week & Calendar Calculators
Sunrise/Sunset Calculator
Day of Week & Calendar Calculators
