However, every year divisible by 100 is not a leap year.
However, every year divisible by 400 is a leap year after all.
To this day, most of the world uses his Gregorian calendar.
Before today’s Gregorian calendar was adopted, the older Julian calendar was used.
By the time he reformed the Julian calendar in 1582 (using the observations of Christopher Clavius and Johannes Kepler), it had drifted 10 days off course.
It was decreed by Pope Gregory XIII in a papal bull on 24 February 1582.
This bull is named “Inter Gravissimas” after its first two words.
In the Gregorian calendar, the tropical year is approximated as 365 is achieved by having 97 leap years every 400 years.
The Gregorian calendar has 97 leap years every 400 years: Every year divisible by 4 is a leap year.