Leap Year List

What the leap year list does

Sometimes one year is not the question. You want all the leap years across a stretch of time. This tool does exactly that. Give it a start year and an end year, and it lists every leap year that falls between them. Instead of checking years one by one, you get the whole set in a single pass.

How to use it

1. Start Year. The first year of the span.
2. End Year. The last year of the span.

Press Calculate for the full list of leap years in that range. Press Reset to clear the boxes.

How the list is built

It walks through every year from your start to your end and keeps the ones that pass the leap-year rule, which is a year divisible by 4, with century years also needing to divide by 400. The years that clear the rule go into the list, in order, and the rest are left out. Because it checks each year individually, it handles the century exceptions correctly across long spans, so a range that crosses a year like 1900 or 2100 leaves those out as it should.

Why a whole list is useful

Seeing the leap years laid out across a range is handy in ways a single check is not. If you are auditing a set of dates in a spreadsheet, the list tells you which years could legitimately contain a 29th of February. If you are building a calendar or a schedule that runs for years, you can see the leap years coming in advance. And for a bit of history or curiosity, a span of decades shows the steady rhythm of the calendar in one view.

Roughly one year in four

Across most ranges, about a quarter of the years come back as leap years, since they land every four years. So a 40-year span will usually give you around 10 of them. The count dips very slightly below a clean quarter over very long ranges, because three out of every four century years are skipped by the divide-by-400 part of the rule. For ordinary spans of a few decades, though, the one-in-four pattern is what you will see.

Questions people ask

Can it list leap years across any range?

Yes. Enter any start and end year and it returns every leap year between them, including the endpoints if they qualify.

Does it handle century years correctly?

Yes. It applies the full rule, so century years that do not divide by 400, like 1900 and 2100, are correctly left out of the list.

How many leap years are in a range?

Roughly one in four, since they fall every four years. A 40-year span usually holds about 10, with a tiny reduction over very long ranges due to the skipped century years.

What if I only want to check one year?

For a single year, a leap year calculator with a check mode is the quicker fit. This tool is built for getting the whole list across a span.

References

1. U.S. Naval Observatory, Astronomical Applications Department: Leap Years. https://aa.usno.navy.mil/faq/leap_years