Leap years and age calculation

The Earth takes about 365.2422 days to orbit the Sun. The leap year fixes the calendar drift — but the rule is more nuanced than "every four years".

The actual rule

Divisible by 4, unless divisible by 100, unless divisible by 400. So 2000 was a leap year; 1900 was not.

Why this matters

Naively dividing total days by 365 accumulates error every leap year — about 20 days over an 80-year lifespan. Walking the calendar avoids this.

If your birthday is February 29

About 1 in 1,461 people is born on Feb 29. In non-leap years the calculator treats Feb 28 as the substitute birthday, so countdowns and milestones still work.

Days vs years

From January 1, 2000 to January 1, 2024 is exactly 24 years and 8,766 days — six more than 24 × 365 because of intervening leap years.

In practice

The live calculator handles all of this. Try a Feb 29 birth date — the next-birthday math adjusts automatically.

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