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Check any year, and see why it is or isn't a leap year.
Enter a year to check.
Leap year if (year % 4 == 0 and year % 100 != 0) or year % 400 == 0
Years divisible by 100 are skipped unless they are also divisible by 400, which is why 1900 was not a leap year but 2000 was.
Checking the year 2100.
2100 is not a leap year: it is divisible by 100 but not by 400, so February has 28 days.
A solar year is about 365.2422 days. Adding a day every four years, with the century corrections, keeps the calendar aligned with the seasons.
No. It is divisible by 100 but not by 400, so the leap day was skipped.
The Gregorian rule drifts by roughly one day every 3,200 years, which is why no further correction is currently applied.
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