How many weeks are there in a year? For most purposes, all you need to know is that there are 52 full weeks in a year.
To be more precise however, there are actually 52.18 weeks in a year. This is because a year, one revolution of the Earth around the Sun, consists of 365.242 days. There are seven days in a week, and 365.242 divided by 7 equals 52.18.
A leap year occurs once every four years, and contains an extra calendar day. Thus, there are 52.29 weeks in a leap year.