Quick answer
Under Gregorian rules, years divisible by 4 have February 29, except century years. A century year has February 29 only if it is divisible by 400.
Step by step
- Check whether the year is divisible by 4. If it is, check the century exception.
- If it ends in 00, divide it by 400. A whole-number result means a leap year.
- When counting a range that crosses February 29, include the extra date using the same endpoint convention as the rest of the range.
Worked examples
Check century years
2000 is divisible by 400 and is a leap year. 1900 and 2100 are divisible by 100 but not 400, so they are common years.
Compare matching ranges
Feb 28 to Mar 1 is 1 elapsed day in 2027 and 2 elapsed days in 2028. The inclusive counts are 2 and 3, respectively.
What to check
Adding a calendar year to Feb 29 can require a policy for the target date. Adding a fixed number of days is a separate operation.
Related guides
Sources
See the calculation methodology or report an error.