# How many Days are in a Year?

Calendars that are basically dependent on the revolution of our around the sun feature in the calendar cycle of 400 years. This calendar cycle is of 400 years and comprises 303 common years and 97 leap years.

A Leap year is divisible by 4, usually comes every fourth year and should have made 100 of these 400 years but the leap years which are divisible by 100 but are not divisible by 400 are not considered leap years. i.e in a 400-year cycle the year number 100, 200, and 300 are actually divisible by 4 and should be leap year but as these years are divisible by 100 but indivisible by 400 so these are not considered leap year and contains 365 days as the common year has.

## Days in a year calculation

### Gregorian calendar year

One calendar common year has 365 days:

1 common year = 365 days

One calendar leap year has 366 days:

1 leap year = 366 days

Leap year occurs every 4 years, except for years that are divisible by 100 and not divisible by 400.

So the mean length of the Gregorian calendar year is:

1 mean year = (365+1/4-1/100+1/400) days = 365.2425 days

### Julian year

Julian year is used for astronomical calculations (light year definition).

One Julian year has 365.25 days:

1 year = 365.25 days

### Sidereal year

One sidereal year is the time it takes the Earth to do a single rotation around the sun.

One sidereal year has 365.25636 days:

1 year = 365.25636 days

### Tropical year

One tropical year is the time it takes the Earth to complete a single cycle of the 4 seasons.

One tropical year has 365.242189 days:

1 year = 365.242189 days

How long is 1 year exactly?