Leap Year Calculator

Check if any year is a leap year and discover the astronomical rules that govern our calendar. Perfect for finding leap years, understanding leap day birthdays, and calendar calculations.

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How to Use the Leap Year Calculator

This calculator instantly determines whether any year is a leap year and explains the astronomical rules behind the calculation.

Enter a year between 1 and 9999 in the input field above.
See instant results — the calculator immediately shows if it's a leap year or not.
Read the explanation — learn exactly which leap year rule applies to your entered year.
View next leap years — see the next 10 leap years from your entered year.
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What Is a Leap Year? Understanding the Calendar System

A leap year is a calendar year that contains 366 days instead of the usual 365 days. The extra day, February 29, is added to keep our calendar synchronized with Earth's orbit around the Sun. Without leap years, our calendar would slowly drift out of alignment with the seasons, eventually causing summer to occur in what we currently call winter months.

The Earth takes approximately 365.2422 days to complete one full orbit around the Sun, not exactly 365 days. This means that each regular year is about 0.2422 days (nearly 6 hours) shorter than one complete solar orbit. If we didn't add leap years, these extra hours would accumulate, and after about 100 years, the calendar would be off by roughly 24 days. Leap years compensate for this discrepancy by adding an extra day approximately every four years.

The concept of leap years dates back to the Julian calendar introduced by Julius Caesar in 45 BCE, which added February 29 every four years. However, this system slightly overcorrected the calendar drift. In 1582, Pope Gregory XIII introduced the Gregorian calendar with more refined leap year rules, which is the calendar system used by most of the world today. The Gregorian system achieves remarkable accuracy by using a complex set of divisibility rules.

People born on February 29 are called "leaplings" or "leapers." They only experience their actual birth date once every four years, though they still age normally. Many leaplings celebrate their birthdays on February 28 or March 1 during non-leap years. The odds of being born on leap day are approximately 1 in 1,461, making it the rarest birthday to have.

Leap Year Rules: How to Determine If a Year Is a Leap Year

The complete leap year rules are: A year is a leap year if it is divisible by 4, except for years divisible by 100, which are not leap years, unless they are also divisible by 400, in which case they are leap years. These three rules work together to keep our calendar accurate to within one day every 3,236 years.

Rule 1 - Divisible by 4: If a year is evenly divisible by 4, it is generally a leap year. For example, 2024, 2028, and 2032 are all divisible by 4, so they are leap years. This basic rule accounts for the fact that Earth's orbit is roughly one-quarter day longer than 365 days. Applying this rule alone adds one day every four years, which equals 0.25 days per year—close to the actual 0.2422-day discrepancy.

Rule 2 - Exception for Century Years (Divisible by 100): If a year is divisible by 100, it is not a leap year, even if it's divisible by 4. For example, 1900, 2100, 2200, and 2300 are all divisible by 100, so they are not leap years. This exception removes three leap years every 400 years to correct for the slight overcorrection of the divisible-by-4 rule. Without this rule, we would add too many leap years and our calendar would drift in the opposite direction.

Rule 3 - Exception to the Exception (Divisible by 400): If a year is divisible by 400, it is a leap year, even though it's also divisible by 100. For example, 2000 and 2400 are divisible by 400, so they are leap years despite being century years. This third rule fine-tunes the system, adding back one leap year every 400 years to achieve near-perfect accuracy with Earth's actual orbital period.

Mathematical Formula: You can express the leap year rules as: (year % 4 == 0) AND ((year % 100 != 0) OR (year % 400 == 0)). This logical formula captures all three rules in a single statement. If this expression evaluates to true, the year is a leap year; if false, it's not. Programmers use this formula in date calculation software worldwide.

How to Calculate Leap Year: Step-by-Step Examples

Example 1 - Regular leap year (2024): Check if 2024 is divisible by 4: 2024 ÷ 4 = 506 (yes, evenly divisible). Check if 2024 is divisible by 100: 2024 ÷ 100 = 20.24 (no, not evenly divisible). Since 2024 is divisible by 4 but not by 100, it passes Rule 1 and doesn't trigger the Rule 2 exception. Result: 2024 is a leap year with 366 days and includes February 29.

Example 2 - Century year that's not a leap year (1900): Check if 1900 is divisible by 4: 1900 ÷ 4 = 475 (yes, evenly divisible). Check if 1900 is divisible by 100: 1900 ÷ 100 = 19 (yes, evenly divisible). Check if 1900 is divisible by 400: 1900 ÷ 400 = 4.75 (no, not evenly divisible). Since 1900 is divisible by 100 but not by 400, Rule 2 exception applies and overrides Rule 1. Result: 1900 is not a leap year; it has only 365 days.

Example 3 - Century year that is a leap year (2000): Check if 2000 is divisible by 4: 2000 ÷ 4 = 500 (yes). Check if 2000 is divisible by 100: 2000 ÷ 100 = 20 (yes). Check if 2000 is divisible by 400: 2000 ÷ 400 = 5 (yes, evenly divisible). Since 2000 is divisible by 400, Rule 3 exception applies, overriding Rule 2. Result: 2000 is a leap year with 366 days, including February 29.

Example 4 - Regular non-leap year (2023): Check if 2023 is divisible by 4: 2023 ÷ 4 = 505.75 (no, not evenly divisible). Since 2023 fails the first test, we don't need to check further rules. Result: 2023 is not a leap year; it has 365 days and no February 29.

Why Do We Have Leap Years? The Astronomical Reason

We have leap years because Earth's orbital period around the Sun is not exactly 365 days—it's approximately 365.2422 days, or 365 days, 5 hours, 48 minutes, and 46 seconds. This fractional portion means that if we used a calendar with exactly 365 days every year, the calendar would fall behind the astronomical seasons by about one day every four years. Over centuries, this drift would cause significant seasonal misalignment.

Without leap years, the calendar date of the spring equinox (around March 20) would gradually move earlier in the calendar year. After 100 years without leap year corrections, spring would arrive about 24 days earlier than expected. After 700 years, the seasons would be completely reversed—spring would occur in September, summer in December, fall in March, and winter in June. This would create chaos for agriculture, navigation, religious observances, and daily life.

The leap year system is Earth-specific. Other planets would need different leap year rules because their orbital periods differ from ours. For example, Mars takes about 687 Earth days to orbit the Sun, while Venus takes 225 Earth days. If humans ever establish permanent settlements on other planets, we'll need to develop new calendar systems with different leap year rules tailored to each planet's unique orbital characteristics.

Interestingly, the Gregorian calendar's leap year system is not perfect—it still gains about one day every 3,236 years compared to Earth's actual orbit. Some astronomers have proposed further refinements, such as making years divisible by 4,000 not leap years. However, the current system is accurate enough for all practical purposes, and any adjustments won't be needed for over a millennium.

Leap Day and Leap Year Babies: February 29 Facts

Leap day, February 29, occurs only in leap years, making it the rarest calendar date. People born on February 29 are often called "leaplings," "leapers," or "leap year babies." There are approximately 5 million leaplings worldwide, representing about 0.07% of the global population. The odds of being born on leap day are roughly 1 in 1,461, assuming births are evenly distributed across all days of the year.

Leaplings face unique challenges with official documentation, age verification, and birthday celebrations. Most leaplings celebrate their birthdays on February 28 or March 1 during non-leap years. Legally, different jurisdictions handle leap day birthdays differently. In most countries, leaplings are considered to have aged one year on March 1 in non-leap years for legal purposes like driving licenses, voting eligibility, and age of majority.

Some famous people born on leap day include motivational speaker Tony Robbins (February 29, 1960), rapper Ja Rule (February 29, 1976), and motivational speaker and author Dennis Farina (February 29, 1944). The town of Anthony, Texas, and Anthony, New Mexico, both claim to be the "Leap Year Capital of the World" and hold leap year birthday festivals every four years, attracting leaplings from around the globe.

There are some interesting leap day traditions around the world. In Ireland, a long-standing tradition says that women can propose marriage to men on leap day, and men who refuse must buy the woman 12 pairs of gloves to hide her embarrassment of not having an engagement ring. In Greece, it's considered bad luck to marry during a leap year, particularly on leap day itself. Some cultures view leap years as times of change, unpredictability, or unusual events.

Leap Year History: From Julius Caesar to Modern Times

The concept of intercalation (adding extra days to a calendar) dates back to ancient civilizations. The ancient Egyptians used a 365-day calendar with no leap years, causing their calendar to drift against the seasons over time. Ancient Babylonians used a lunar calendar and periodically added entire months to realign with the solar year. The Roman calendar before Julius Caesar was a complex, politically manipulated system that had fallen significantly out of sync with the seasons.

In 45 BCE, Julius Caesar introduced the Julian calendar with the advice of the Alexandrian astronomer Sosigenes. This calendar established the 365-day year with a leap day added every four years, creating an average year length of 365.25 days. The Julian calendar was a massive improvement and was used throughout the Roman Empire and later Christian Europe for over 1,600 years. However, it slightly overcompensated, adding about 11 minutes and 14 seconds too much per year.

By 1582, the Julian calendar had drifted about 10 days ahead of the astronomical seasons. Pope Gregory XIII commissioned a calendar reform, resulting in the Gregorian calendar we use today. The reform included two major changes: First, 10 days were removed from October 1582 (October 4 was followed by October 15). Second, the refined leap year rules (divisible by 400) were introduced to prevent future drift. Catholic countries adopted it immediately, but Protestant and Orthodox countries resisted for centuries.

The adoption of the Gregorian calendar varied worldwide: Spain, Portugal, and Italy adopted it in 1582; Great Britain and its colonies (including America) switched in 1752, removing 11 days from September; Russia didn't adopt it until after the 1917 Revolution; Greece held out until 1923; and some Orthodox churches still use the Julian calendar for religious purposes. This gradual adoption created historical confusion—some historical figures have two different birth dates depending on which calendar system is used.

People Also Search For

Is 2024 a leap year?

Yes, 2024 is a leap year. It is divisible by 4 (2024 ÷ 4 = 506), and it is not a century year, so it qualifies as a leap year under the standard leap year rule. The year 2024 has 366 days, including February 29. If you were born on February 29, 2024, you are a leapling, and your next "real" birthday will be on February 29, 2028.

Is 2025 a leap year?

No, 2025 is not a leap year. When you divide 2025 by 4, you get 506.25, which is not a whole number. Since 2025 is not evenly divisible by 4, it does not meet the basic requirement for a leap year. The year 2025 has only 365 days, and February ends on the 28th. The next leap year after 2025 will be 2028.

Is 2026 a leap year?

No, 2026 is not a leap year. Dividing 2026 by 4 gives 506.5, which is not a whole number. Since 2026 is not evenly divisible by 4, it cannot be a leap year. The year 2026 will have 365 days with February ending on February 28. You'll need to wait until 2028 for the next leap year.

Was 2000 a leap year?

Yes, 2000 was a leap year. Even though 2000 is a century year (divisible by 100), it is also divisible by 400 (2000 ÷ 400 = 5), which makes it a leap year according to the exception to the exception rule. The year 2000 had 366 days and included February 29. This is different from 1900, which was not a leap year, and 2100, which will not be a leap year.

Was 1900 a leap year?

No, 1900 was not a leap year. Although 1900 is divisible by 4, it is also divisible by 100 but not by 400 (1900 ÷ 400 = 4.75). According to the leap year rules, century years must be divisible by 400 to be leap years. Since 1900 fails this test, it was a common year with only 365 days and no February 29.

When is the next leap year?

If you're reading this in 2026, the next leap year is 2028. Leap years occur every four years in most cases, following the pattern: 2024, 2028, 2032, 2036, 2040, 2044, 2048, 2052, 2056, 2060, and so on. The next leap year from any given year can be found by checking which of the next three years is divisible by 4 (unless you're near a century year, in which case you need to apply the full leap year rules).

How many days in a leap year?

A leap year has 366 days, which is one more day than a regular year's 365 days. The extra day is added as February 29. In a leap year, January has 31 days, February has 29 days (instead of 28), and the remaining months have their standard lengths. The 366 days equal 52 weeks plus 2 days, which means a leap year always starts and ends on different days of the week.

What is a leap year baby?

A leap year baby (also called a "leapling" or "leaper") is someone born on February 29. Because February 29 only exists in leap years, these individuals only have their "real" birthday once every four years. In non-leap years, they typically celebrate on February 28 or March 1. The odds of being born on leap day are approximately 1 in 1,461, making it the rarest birthday to have.

Frequently Asked Questions

How do I know if a year is a leap year?

Check if the year is divisible by 4. If yes, it's usually a leap year. However, if the year is also divisible by 100, it's not a leap year unless it's also divisible by 400. For example, 2024 is a leap year (divisible by 4), 1900 was not (divisible by 100 but not 400), and 2000 was (divisible by 400).

Why are leap years necessary?

Leap years are necessary because Earth takes approximately 365.2422 days to orbit the Sun, not exactly 365 days. The extra ~0.2422 days (about 6 hours) accumulate each year. Adding a leap day every four years compensates for this difference and keeps our calendar aligned with the astronomical seasons.

What happens if you're born on February 29?

People born on February 29 are called "leaplings." They only have their actual birth date once every four years. In non-leap years, they typically celebrate on February 28 or March 1. Legally, they age normally—most jurisdictions consider their birthday to be March 1 in non-leap years for official purposes.

Why wasn't 2100 chosen as a leap year?

The year 2100 will not be a leap year because it's divisible by 100 but not by 400. This exception to the leap year rule prevents overcorrection—adding a leap year every 4 years is slightly too much, so we skip leap years on most century years (except those divisible by 400 like 2000 and 2400).

How often do leap years occur?

Leap years occur approximately every 4 years. Over a 400-year period, there are exactly 97 leap years (not 100), because century years divisible by 100 but not 400 are skipped. This averages to 0.2425 leap years per year, which closely matches Earth's orbital period of 365.2422 days.

What's the difference between Julian and Gregorian leap years?

The Julian calendar (introduced by Julius Caesar) made every year divisible by 4 a leap year, creating an average year of 365.25 days. The Gregorian calendar (introduced in 1582) refined this by skipping leap years on century years not divisible by 400, creating an average year of 365.2425 days—much closer to Earth's actual orbital period.

Is the leap year calculator accurate for historical dates?

This calculator uses Gregorian calendar rules, which were adopted in 1582. For dates before 1582, different regions used the Julian calendar or other systems. The calculator will correctly identify which years would be leap years under Gregorian rules, but historical dates may not match if the region was using a different calendar at that time.

Why is February chosen for the leap day?

February was historically the last month of the Roman calendar year (which began in March). Romans typically added intercalary days at the end of their calendar, making February the natural choice. When January and February were later moved to the beginning of the year, the tradition of adding the leap day to February remained.

Can I trust this leap year calculator for programming dates?

Yes, this calculator implements the standard Gregorian calendar leap year algorithm used worldwide in date/time libraries and programming languages. It correctly handles all three rules: divisible by 4, the century exception (divisible by 100), and the 400-year exception. It's suitable for any date calculations from 1 to 9999.

What is the longest gap between leap years?

The longest gap between leap years is 8 years, which occurs when a century year that is not divisible by 400 falls between regular leap years. For example, there were 8 years between the leap year 1896 and the next leap year 1904, because 1900 was not a leap year. This same pattern will occur again from 2096 to 2104.

Will the leap year system ever change?

The current Gregorian leap year system is accurate to within one day every 3,236 years, which is sufficient for all practical purposes. Some scientists have proposed further refinements (such as making years divisible by 4,000 not leap years), but no changes are planned. The system is internationally standardized and deeply embedded in global infrastructure.

How do leap years affect age calculation?

Leap years add one extra day (February 29) to age calculations for anyone alive during that year. If you're calculating someone's age in days, you must account for all leap years that occurred during their lifetime. Our Age Calculator automatically handles leap years to give you exact age in days, accounting for every February 29 you've lived through.

What is a leap second?

A leap second is different from a leap year. Leap seconds are occasional one-second adjustments added to Coordinated Universal Time (UTC) to account for irregularities in Earth's rotation. Unlike leap years (which follow a predictable pattern), leap seconds are announced only about six months in advance and have been added irregularly since 1972. They are not related to the calendar leap year system.

Are leap years the same on other planets?

No, each planet would need its own leap year system based on its unique orbital period. Mars, for example, takes about 687 Earth days to orbit the Sun, and a Martian calendar would require a completely different intercalation system. The concept of leap years is specific to Earth's orbital mechanics and our base-365-day calendar system.

How accurate is the Gregorian calendar?

The Gregorian calendar is remarkably accurate, with an error of only about one day every 3,236 years compared to Earth's actual orbital period. This means it won't need adjustment until approximately the year 5200 CE. It's accurate enough for all historical, legal, and scientific purposes for millennia to come.

Last reviewed: February 2026 — formulas and guidelines verified.