Math Playground
Measurement

Calendar — leap years

Why every fourth year — except some — gets an extra day.

A leap year has 366 days — an extra Feb 29.

Try this
2024
is it a leap year? = 2024 is a LEAP year — 366 days (Feb 29)

The leap-year rule, in order

  • Divisible by 4 → leap year…
  • …UNLESS also divisible by 100 → not a leap year…
  • …UNLESS also divisible by 400 → leap year after all.
  • So 2000 was a leap year, but 1900 and 2100 are not.

Why bother? A year is ≈365.2422 days. Adding one day every 4 years over-corrects slightly; the ÷100 and ÷400 exceptions trim it back. The result drifts by only about one day in 3,000 years.

Your turn

Was 1600 a leap year? Was 1700?

Rules

  • Year divisible by 4: leap year.
  • Except: divisible by 100 but not 400: NOT a leap year.
  • So 2000 was a leap year, 1900 was not.