Also in case you did not know, the leap year is not on even hundreds of years, i.e. 1900 was not a leap year, and neither will 2100 be under the current calenda

Also in case you did not know, the leap year is not on even hundreds of years, i.e. 1900 was not a leap year, and neither will 2100 be under the current calendar. The exception is every four hundred years, which means 2000 was a leap year, as would 1600 have been, and 2400 will be. This means the year is on average 365.2425 days long[1] -- a constant that I've found surprisingly useful to memorise. [1]: Because 365 + 1/4 - 1/100 + 1/400.