Find Common Years

A common year is a standard calendar year with exactly 365 days. It is any year that is NOT a leap year according to the Gregorian rules, meaning it does not contain a February 29th.

A year is a leap year if it’s divisible by 4, EXCEPT century years (divisible by 100), UNLESS they’re also divisible by 400. So 2024 is leap, 2100 is common (century, not divisible by 400), and 2000 was leap (century AND divisible by 400). The tool’s predicate is (y % 4 === 0 && y % 100 !== 0) || y % 400 === 0.

Over any 400-year cycle exactly 97 years are leap and 303 are common – so 24.25% leap, 75.75% common. The Gregorian calendar’s average year length is 365.2425 days, which matches the solar year to within ~26 seconds. Across small ranges the ratio fluctuates; the tool’s stats line shows the percentage for whatever range you entered.

The tool auto-swaps the bounds so you never get an empty result by mistake. The stats line includes “bounds auto-swapped” so you know what happened.

Before October 1582, most of Europe used the Julian calendar, which had a simpler leap rule (every 4 years, no exceptions). This tool uses the Gregorian rule for all years – proleptic for pre-1582 dates. For historical research before 1582, the year classification may differ from what a contemporary calendar would say.

It’s a UI bound, not a math limit. The algorithm is pure modulo arithmetic with no Date involved, so it works for any integer in theory. The cap keeps inputs sensible – a million-year range would produce a huge text dump but technically work.

Two grouped lists: “Common (N):” followed by every common year separated by commas, then “Leap (M):” followed by every leap year. Useful for side-by-side comparison without running the tool twice.

Yes, completely! This Common Year Finder operates 100% locally directly from your browser’s (client-side) engine. No calculation data is transmitted across the internet to our servers preserving absolute privacy.