> As a rule of thumb, leap days come around every four years. But there are exceptions to this rule. For example, at the turn of every century we miss a leap year. Even though the year is divisible by four, we don't add a leap day in the years that end in 00. But there's an exception to this rule too. If the year is a multiple of 400 then we do add in an extra leap day again. At the turn of the millennium, despite being divisible by 100, the year 2000 did, in fact, have a 29 February because it was also divisible by 400.
https://www.bbc.com/future/article/20240228-leap-year-the-im...