The number of days in a year varies depending on whether it is a normal year or a leap year. A normal year is any year that does not contain February 29th, which is leap day. Throughout the 21st century, there will be 366 days in every leap year and 365 days in every other year (excluding those divisible by 400).
A normal year
A normal year has 365 days, and every four years it is leap year. On leap years, February 29th is a day that comes only once every four years.
A normal year looks like this:
A leap year
A leap year is a year that has 366 days. Thats right, in every four years (except those divisible by 100 or 400), the extra day is added to February 29th. This means that February will have 29 days instead of 28!
Leap years happen because the calendar isnt perfect, so it needs some adjustments from time to time. To fix this problem, we add an extra day every four years—the same amount of time it takes for our planet to revolve once around its axis (and therefore go around its sun).
In order for a non-leap year to become a leap year, it must be divisible by 4 but not by 100 or 400; if that condition isnt met then instead of being added onto February 29th it gets pushed into December 31st (making December 31st no longer fall on any particular date).
The number of days in a year is 365 unless it is a leap year.
The number of days in a year is 365 unless it is a leap year. In a leap year, February has an extra day that is added to the end of February. The extra day is February 29th, which means that there are 366 days in this particular month.
Conclusion
The number of days in a year is 365 unless it is a leap year.