What does this tool do?
A leap year adds 29 February to keep the calendar aligned with the seasons. The Gregorian rule skips most century years, while the Julian rule treats every fourth year as a leap year.
The Formula
Gregorian leap = divisible by 4, except centuries not divisible by 400Frequently Asked Questions
Is 1900 a leap year?
No under the Gregorian rule, because it is a century not divisible by 400. Under the Julian rule it would be a leap year.
How is the next leap year found?
The calculator checks subsequent years with the selected rule. The gap is usually four years, but a century boundary can make it eight.