When does February 29 occur?

February 29 occurs only in leap years, which are years that are evenly divisible by 4 AND (not evenly divisible by 100 UNLESS also evenly divisible by 400).

For example, 1996, 2000, 2004 and 2096 are leap years, and 1900, 2001, 2002 and 2100 are not.