What are the rules for a year to be a leap year?
Quick Answer: A year is a leap year if it is divisible by 4. However, if it is divisible by 100, it must also be divisible by 400 to be a leap year. Otherwise, it is a common year.
Leap years keep our calendar aligned with Earth's orbit around the Sun. Since a full orbit takes about 365.25 days, we add an extra day every four years to catch up.
But not every year divisible by 4 is a leap year. Years divisible by 100 are exceptions unless they can be divided by 400. That's why 2000 was a leap year but 1900 was not.