What week number is it?
Today’s ISO-8601 week number, the week for any date you choose, and a full table of week start and end dates for the year.
| Week | Monday | Sunday |
|---|
Runs entirely in your browser. Nothing you enter is sent to a server.
How ISO week numbers work
Under ISO 8601, weeks start on Monday and week 1 is the week containing the year’s first Thursday (equivalently, the week with 4 January). So a year has 52 or 53 weeks, and the first days of January can belong to the last week of the previous year — 1 January 2027, a Friday, is in week 53 of 2026.
ISO weeks are standard in Europe and common in business planning, manufacturing and payroll. Some North American calendars count weeks from Sunday and start week 1 on 1 January, so numbers can differ by one — check which system your workplace uses.
Need the date a number of weeks from now? Use the date calculator.
Frequently asked questions
What week number is it today?
It’s shown at the top of this page, calculated from your device’s date.
How many weeks are in a year?
52 or 53 ISO weeks. Years starting on a Thursday (or leap years starting on a Wednesday) have 53.
Why does my calendar show a different week?
Some calendars start weeks on Sunday or count 1 January as week 1. This page uses the ISO 8601 standard.