It is very easy to find or identify leap years. Leap years have 366 days and they occur every 4 years.
For example, 1916, 1920, 1924, and 1928 are consecutive leap years.
1920 had 366 days and this means that February had 29 days in that year. February had 28 days in 1917, 1918, and 1919.
Take a close look at these four consecutive leap years and look for a pattern. Did you notice that these four leap years can be divided by 4?
1916 / 4 = 479
1920 / 4 = 480
1924 / 4 = 481
1928 / 4 = 482
Therefore, as a rule of thumb, if a year can be divided by 4, it is a leap year.
The divisibility rule of 4 can make it a lot easier to determine if a year is a leap year.
A number is divisible by 4 if the number represented by its last two digits is divisible by 4.
For instance, 1916 is divisible by 4 because 16 is divisible by 4.
By the same token, 1920 is divisible by 4 because 20 is divisible by 4.
Now, you are ready to quickly tell if a year is a leap year.
In 1988, 88 divided by 4 is equal to 22, so 1988 is a leap year.
In 2022, 22 divided by 4 is equal to 5.5, so 2022 is not a leap year. In fact, the next leap year after 2020 is 2024 since in 2024, 24 can be divided by 4.
Will the year 2100 be a leap year? No, sorry! Although 2100, can be divided by 4, 2100 is not a leap year.
The leap year was created to make sure that our calendar is in line with the time it takes the earth to revolve around the sun.
It takes the earth about 365.2425 days to revolve around the sun. Therefore, using only 365 days on our calendar is not completely accurate.
To solve this problem, every four years, we can just add 1 day to February to make it 29 days.
This means that every year, 1 / 4 or 0.25 day is added.
What we are doing here is saying that each year has 365.25 days.
However, this also creates another issue since we added a little too much.
365.25 - 365.2425 = 0.0075
If 0.0075 day extra is added each year, what happens after 400 years?
0.0075 × 400 = 3
Every 400 years, we add 3 days extra. In order to balance things out, there are 3 years that cannot be leap years during the 400 years.
From the year 2000 to the year 2399, there are 400 years.
2000 is a leap year. Therefore, 2100, 2200, and 2300 cannot be leap years.
From 2000 all the way to 2096, there will be 25 leap years.
2100 is not a leap year
From 2104 all the way to 2196, there will be 24 leap years.
2200 is not a leap year
From 2204 all the way to 2296, there will be 24 leap years.
2300 is not a leap year.
From 2304 all the way to 2399, there will be 24 leap years.
25 + 24 + 24 + 24 = 97
Therefore, there are 97 leap years in 400 years. For the years 2100, 2200, and 2300, February will not have 29 days for those of course who will be living on the earth at that time.