What this calculator does
Every input on this leap year calculator maps to a real decision, so the output is something you can act on immediately, not a rough ballpark you'll have to double-check elsewhere.
Leap year rule: divisible by 4, except centuries unless by 400.
How to use the Leap Year Calculator
- Enter your values in the fields on the left.
- Results update automatically.
- Use action buttons to copy, share or print.
The formula
leap = (y%4==0 && y%100!=0) || y%400==0
Worked example
2024 leap; 1900 not; 2000 leap.
Common mistakes
- Centuries confusion
- Off-by-one on Feb 29
- Julian vs Gregorian
When to use it
Use for calendars and date math.
Pro tips for the Leap Year Calculator
- Save your favorite scenarios by clicking the star icon — they're stored locally, no account needed.
- For big decisions, run best-case, expected, and worst-case scenarios and compare the breakdowns side by side.
- Copy the result to paste it directly into email, Notion, or a spreadsheet cell.
Frequently asked questions
›Why every 4?
Solar year is ~365.25 days.
›Century exception?
Adjusts for 365.2425 real length.
›Leap seconds?
Different — added for Earth rotation.
›Feb 29 birthday?
Celebrated Feb 28 or Mar 1 in common years.
›Julian calendar?
Different rule — every 4 years, always.
›How accurate is this leap year calculator?
The formulas match the standard textbook definition shown above. Rounding is applied only for display; underlying computation uses full floating-point precision. For regulated time & date decisions, always confirm with a qualified professional.
›Does the Leap Year Calculator store the numbers I enter?
No. All math runs locally in your browser — nothing is sent to a server, and closing the tab discards the inputs unless you save them to favorites.
Embed this calculator
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