@twothecat You can ask another questions or you can do some reading. This is a small excerpt “The Gregorian calendar modified the Julian calendar’s regular cycle of leap years, years exactly divisible by four, including all centurial years, as follows: Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100; the centurial years that are exactly divisible by 400 are still leap years. For example, the year 1900 is not a leap year; the year 2000 is a leap year.” The difference is about 11 minutes per year.