Leap Year Calculator - Test, Find & List Years

A leap year is a Gregorian calendar year that contains 366 days instead of the usual 365, with February 29 added as the extra day. This calculator returns a Yes/No verdict, the total days in the year, the next and previous match, and a list of every qualifying year in your custom range, which helps you plan birthdays, anniversaries, payroll cycles, and historical events that fall on February 29.

• • February 29 birthdays: Confirm whether a year contains February 29 so you can schedule a leap-day birthday, plan gifts, or compute how many years until the next celebration.
• • Anniversary planning: Identify which years between two anniversaries fall on Feb 29 when planning milestones, retirement dates, or wedding anniversary countdowns.
• • Payroll and accounting cycles: Count the qualifying years in a multi-year span to estimate the extra work days in February and refine labor or revenue projections.
• • Historical and genealogical research: Verify whether a historical year had a Feb 29 to align civil and family tree records with the correct day count.

The extra day in February exists because Earth takes about 365.2425 days to orbit the Sun, so a plain 365-day calendar drifts by roughly a quarter day every year. The rule is: a year qualifies if it is divisible by 4, except for years divisible by 100, except for years divisible by 400. That single nested rule explains every common case (2024 qualifies) and every surprise case (1900 and 2100 do not, while 2000 does). Enter any year from 1 to 9999, then use the range fields to list every match between two milestones.

To convert the qualifying-year count in a range into the actual number of days between two dates, use the Days Between Dates Calculator with your two boundary dates.

The calculator applies the Gregorian 4-100-400 rule to the year you enter, then increments or decrements to find the next and previous match, and finally scans the range for every qualifying year in between.

• y (year): The Gregorian calendar year you want to test, from 1 to 9999.
• y % 4: Remainder when the year is divided by 4. The rule starts with checking whether the year is divisible by 4.
• y % 100: Remainder when the year is divided by 100. Used to exclude century years that are not divisible by 400.
• y % 400: Remainder when the year is divided by 400. Century years divisible by 400 stay in the list despite the % 100 rule.

For the year test, the calculator computes y % 4, y % 100, and y % 400. The result is true when y is divisible by 4 and not by 100, OR when y is divisible by 400. To find the next match, it increments the year by 1 and reruns the test until it returns true. For the range scan, it normalizes the bounds (swaps if start is greater than end) and runs the test for every integer in the inclusive range.

According to U.S. Naval Observatory, the Gregorian rule is that years evenly divisible by 4 are leap years, except for centurial years that are not evenly divisible by 400, which makes 1700, 1800, 1900, and 2100 common years but 1600, 2000, and 2400 leap years.

Once you know the qualifying years in a span, feed the boundary dates into the Years Between Dates Calculator to confirm the fractional year and total day count for the same span.

Four ideas cover everything you need to understand the result, from the simple every-four-years rule to the 400-year cycle that fixes the calendar drift.

A year qualifies if it is divisible by 4, except for century years (divisible by 100) that are not divisible by 400. The 400-year cycle keeps the rule within seconds of the tropical year (about 365.24219 days). Quick examples: 2024 qualifies, 2100 does not, 2000 does.

When you need to add or subtract days, months, or years from a specific calendar date, the Date Calculator complements this rule with general date arithmetic.

Enter the year you want to test and the range you want to scan. Results update in real time as you type.

1. 1 Enter the year to test: Type any four-digit Gregorian year in the first input. Use 2026 to check the current year, 2024 to verify a known case, or 2100 to see the century exception in action.
2. 2 Set the range start: Enter the first year of the inclusive range you want to scan. Use a past year for a historical count, or a future year to start a forward-looking scan.
3. 3 Set the range end: Enter the last year of the inclusive range. If you accidentally set it before the start year, the calculator swaps the bounds automatically and uses the corrected range in the result.
4. 4 Read the verdict: Check the Verdict row for Yes or No, and the Days in year row for 365 or 366. These two answers always match.
5. 5 Find the next and previous match: Use the Next match and Previous match rows to plan the closest qualifying year on either side of your test year.
6. 6 Count and list the range: Review the Matches in range count and the comma-separated list to count qualifying years across a multi-year span such as a 10-year career window or a 30-year mortgage term.

Suppose you want to schedule a Feb 29 birthday party for someone born on Feb 29, 2000. Enter 2026 to confirm the current year is not a qualifying year, set the range to 2026-2036, and read the list (2028, 2032, 2036) to plan the next three celebrations.

If you are planning around a February 29 birthday, the Birthday Calculator returns the day of the week for each upcoming Feb 29 celebration.

Automating the 4-100-400 rule removes the most common leap-year mistakes, especially the surprise century exception.

• • Catches century exceptions: Highlights years such as 1900 and 2100 that look like qualifying years under the simple every-four-years rule but are not, so scheduling around Feb 29 stays accurate across centuries.
• • Counts multi-year spans: Returns an integer count of qualifying years in any custom range, useful for payroll planning, anniversary tracking, and academic calendars.
• • Locates nearest leap day: Surfaces the next and previous match in a single click, so you can plan Feb 29 events without scanning a calendar by hand.
• • Lists every match: Provides a comma-separated list of every qualifying year in the range, capped to keep the panel readable.
• • Range bounds auto-corrected: Detects reversed start and end years and normalizes the range before scanning.

For everyday planning, the count and list confirm how many February 29 days fit in a span, and the verdict feeds directly into date math such as total days between two dates.

Pair this tool with an age or birthday calculator to convert Feb 29 birthdays into clear year counts. A 30-year mortgage contains either 7 or 8 February 29 days depending on which 30-year window you pick.

Pair the next qualifying year with the Age Calculator to see how old someone will be on their next February 29 birthday in years, months, and days.

The same inputs can produce different human experiences even when the math is identical, so it helps to know which factors shape the answer.

• • This calculator applies the Gregorian rule, not the Julian rule that some countries used before 1582. Use a Julian-specific tool for dates before the Gregorian reform.
• • Extra February days and leap seconds are unrelated: the extra day accounts for calendar drift over the tropical year, while leap seconds are occasional sub-second adjustments managed by the International Earth Rotation Service.

Remember that 'leap day' refers to February 29, not the start of a new year. The 400-year cycle makes the Gregorian calendar very accurate over the long term, but the average year length of 365.2425 days is still about 26 seconds longer than the true tropical year, which is why leap-second adjustments exist.

According to Wikipedia, Leap second, leap seconds are not introduced on a regular schedule because variations in the length of the day are not entirely predictable, which is separate from the leap day in the Gregorian calendar.