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How Many Weeks Are in a Year (52 or 53)
Find out how many ISO weeks a year has — 52 or 53. Under ISO-8601 most years have 52 weeks, but a year has 53 when 1 January is a Thursday, or when it is a leap year and 1 January is a Wednesday. By that rule 2026 has 53 ISO weeks because 1 January 2026 is a Thursday; the next 53-week years are 2032, 2037, 2043 and 2048, and every other year from 2026 to 2048 has 52. Assuming every year has 52 weeks is a common bug, and these “long” ISO years are exactly where week-numbering breaks. Enter any date and the calculator shows the weeks-in-year for that calendar year alongside the ISO week and the week’s Monday-to-Sunday range, all computed in your browser.
Weeks in year = 53 if Jan 1 is Thursday, or (leap year and Jan 1 is Wednesday); else 52
- 2026 has 53 ISO weeks (1 Jan 2026 is a Thursday)
- Next 53-week years: 2032, 2037, 2043, 2048
Frequently asked questions
How many weeks are in a year?
Most years have 52 ISO weeks. A year has 53 when 1 January is a Thursday, or when it is a leap year and 1 January is a Wednesday. So 2026 has 53 ISO weeks; the next 53-week years are 2032 and 2037.
Why do some years have 53 weeks?
Because ISO weeks are whole Monday-to-Sunday blocks anchored to the first Thursday, the 365 or 366 days of a year don’t divide evenly into 52 weeks. When 1 January is a Thursday (or a leap year starting on Wednesday), an extra week 53 is needed.