(1) When the current year is a hundred years, the year divisible by 400 is a leap year, and the year divisible by 400 is a flat year;

(2) When the year is not a whole hundred years, the year divisible by 4 is a leap year, and the year divisible by 4 is a normal year.

February in leap year is 29 days, and in normal year it is 28 days, so leap year has one more day than normal year.