A leap year is a year with one extra day in February. A leap year is 366 days in length (with 29 days in February) rather than the usual 365 days in length (with 28 days in February).

A leap year occurs when the year is divisible by four AND not not divisible one-hundred, unless it is also divisible by four-hundred.

2007 IS NOT a leap year.

2007 is not divisible by 4 (2007 ÷ 4 = 501 remainder 3).

2008 IS a leap year.

2008 is divisible by 4 AND not divisible by 100 (2008 ÷ 4 = 502 remainder 0 AND 2008 ÷ 100 = 20 remainder 8).

2300 IS NOT a leap year.

2300 is divisible by 4 AND is divisible by 100, but not by 400 (2300 ÷ 4 = 575 remainder 0 AND 2300 ÷ 100 = 23 remainder 0 BUT 2300 ÷ 400 = 5 remainder 300).

2400 IS a leap year.

2400 is divisible by 4 AND is divisible by 100 AND is divisible by 400 (2400 ÷ 4 = 600 remainder 0 AND 2400 ÷ 100 = 24 remainder 0 AND 2400 ÷ 400 = 6 remainder 0).