Week Number Calculator
What week number is it?
The ISO week for any date, the US week beside it, the Monday-to-Sunday dates the week covers, and how many weeks the year has.
How this is worked out
- The ISO year can differ from the calendar year: 31 December 2024 falls in ISO week 1 of 2025.
- The page gives the full ISO week date — 2024-W29-2 — which is a valid ISO 8601 date in its own right.
Questions people ask
The things that come up about week number calculators, answered plainly.
Why do two calendars show different week numbers?
Because they use different rules. ISO 8601 starts weeks on Monday and gives week 1 to the week containing the first Thursday. The North American convention starts on Sunday and gives week 1 to the week containing 1 January. They differ by one for part of most years.
How many weeks are in a year?
52 in most years and 53 in some — a year has 53 ISO weeks when it starts on a Thursday, or is a leap year starting on a Wednesday. That happens 71 times in every 400 years.
Related tools
Printable calendars, week numbers, quarters, fiscal years and weekday finders.
ISO Week CalculatorA date to its ISO week-date form and back — `2024-W29-2` — with the ISO year, which is not always the calendar year.
Calendar Week FinderEnter a week number and a year, get the seven dates it covers — and the reverse, a date to its week — with both the ISO and US conventions.
Weekly CalendarSeven days with their dates, week number, and the hours of the day down the side — a week planner you can print or share as a link.
Quarter FinderThe calendar quarter for any date, its start and end, how many days it has, and how far through it you are — plus the same for the next four quarters.