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"rdslon01@mik.uky.edu (rodney d slone) writes: |> Well it will be 2/28/2000 -> 2/29/2000 because if |> year mod 400 == 0 then leap year |> else if |> year mod 100 == 0 then not leap year |> else if |> year mod 4 == 0 then leap year |> else not leap year Looks like the US IRS came up with these rules!" The reason for the rules is of course that the period of rotation is not an exact number of days (think about it, there is no reason the speed of rotation of the earth should have any relation to the speed of rotation around the sun). The length of the year is almost 365.25 days, so a leap day every fourth year is almost right, but it is not exactly 365.25, so higher order corrections are needed. The above statement of rules is nowhere near complete :-)