How do you know if a year is a leap year?

if a year is a multiple of four, then it is a leap year, except for every 100 years. 2100 will not be a leap year for some weird scientifical reason. but every four hundred years, it will be a leap year.

e/i: 2400 will be a leap year.

just to make sure you have the right idea, 2016, 2020, 2024, etc. will all be leap years along with the next four years after each preceeding year until 2100, then the next leap year will be in 2104.