February 29 and leap day
When leap day occurs and how it affects dates and anniversaries.
When February 29 appears
Gregorian leap day occurs in years divisible by four, except century years must also be divisible by 400.
Annual events
Systems need an explicit policy for anniversaries, subscriptions and reminders based on February 29 when the current year has no such date.
Date calculations
Leap day shifts ordinal dates after February and changes annual totals. Calendar-aware date libraries avoid many manual errors.
Related month guides
- Why is February the shortest month? — How Roman calendar history shaped February's unusual length.
- How many days are in each month? — A complete guide to 28-, 29-, 30- and 31-day months.
- How to add or subtract calendar months — Handle month-end dates without overflowing into the wrong month.