Check Common Year
Check Common Year whether any year from 1 to 999999 is a common 365-day year or a 366-day leap year, with Gregorian divisibility breakdown. Free, client-side.
Enter any year 1–999,999 and get a Gregorian leap vs common verdict, divisibility breakdown, and nearest leap-year neighbours.
Divisibility breakdown
Leap rule: divisible by 4, except century years which must also be divisible by 400.
Nearest leap years
How to Use Check Common Year
- Type a year (any integer from 1 to 999,999) in the input field, or hit
Use current yearfor the one we are in right now. - Watch the verdict update after 150 ms - green means common (365 days), amber means leap (366 days).
- Inspect the breakdown card: you will see yes/no rows for divisible-by-4, divisible-by-100, and divisible-by-400. A common year either fails the first rule or trips the century exception.
- Check the nearest leap years card for the closest leap year before and after your input - handy for planning February 29 events.
- Press
Ctrl+Enter(⌘+Enteron Mac) to force a check any time, for example after pasting a number with a decimal. - Copy the summary to your clipboard in one click, or Download a timestamped `.txt` report with the full breakdown.
Frequently asked questions
What is a common year?
A common year is a Gregorian calendar year with exactly 365 days – so February has 28 days instead of 29. Most years are common; only roughly 1 in every 4 is a leap year.
What’s the Gregorian leap-year rule?
A year is a leap year if it is divisible by 4, with one exception: century years (divisible by 100) must also be divisible by 400 to qualify. So 1900 is common, but 2000 is a leap year.
Is my data uploaded anywhere?
No. The year check runs entirely in your browser with a few lines of arithmetic. No fetches, no analytics on the input.
Why is 1900 a common year but 2000 is a leap year?
Both are divisible by 4 and by 100, so both are century years. The extra rule says a century year must also be divisible by 400 to be a leap year. 2000 passes (2000 ÷ 400 = 5); 1900 fails (1900 ÷ 400 = 4.75).
What does the divisibility breakdown show?
Three yes/no rows – divisible by 4, by 100, and by 400 – so you can trace how the tool arrived at the verdict without doing the math yourself.
Why are the nearest leap years useful?
If you are scheduling a February 29 event or checking a contract that depends on a leap year, you often need to know the closest one before or after a given date. The tool finds them with a simple scan.
Does this work for historical years before 1582?
The tool always applies the Gregorian rule. The Julian calendar’s leap rule (every 4 years, no exceptions) was in use before October 1582 in Catholic countries and later elsewhere, so use a dedicated Julian calculator for genuinely historical work.
What is the largest year I can check?
999,999 – a safety cap that keeps the “find nearest leap year” scans fast. A common year check itself is instant at any size; the cap just bounds the scan loop.
Can I check year 0 or negative years?
No. The tool requires a year ≥ 1 because the Gregorian and proleptic-Gregorian conventions disagree on whether a year zero exists. Add an astronomical-year converter if you need BC/BCE support.
Does it work offline?
After the page loads, yes. Everything is static HTML, CSS, and JS – disconnect Wi-Fi and keep checking.