The seasonal year is about 365.2422 days. Counting only 365 would shift dates away from the seasons. Adding a day every four years averages 365.25 days, too many. The Gregorian rule refines that approximation: years divisible by four are leap years, except century years are skipped unless divisible by 400. Thus 1900 was ordinary and 2000 was leap. The 400-year cycle contains 97 leap days and averages 365.2425 days per year. It reduces drift without making the match exact.
Question 3 of 3
Why do we need leap years?
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Original explanatory text informed by the sources below. Last source check: September 17, 2026. These sources are not endorsements of Losslessly.
U.S. Naval Observatory · Leap yearsTokens are units of text counted by a tokenizer. They are not a measure of meaning or difficulty.
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A short before-and-after practice on calendars. No time limit.