How many weeks are in a year?
A year has 52 weeks plus one extra day, or two extra days in a leap year. That is why your birthday moves to the next day of the week each year.
Dividing 365 days by 7 days per week gives 52 weeks with 1 day left over. In a leap year, 366 days divided by 7 gives 52 weeks and 2 days. That small remainder means the calendar shifts each year, so a date that falls on a Monday this year will usually fall on a Tuesday next year.
Some years can contain parts of 53 different weeks. In the ISO week-date system used in business and government in many countries, weeks start on Monday, and a year has either 52 or 53 full numbered weeks. Week 1 is the week that contains the first Thursday of the year.
Working weeks and paydays
Because of the extra days, some years have 53 Fridays or 27 biweekly paydays instead of 26. Businesses and payroll systems need to plan for these years. Calendars repeat exactly every 28 years in most cases, when the pattern of weekdays and leap years lines up again.
Did You Know?
A fortnight is two weeks. The word comes from the Old English for fourteen nights.