Week Number
What week is it today? Find any week number and its dates, in the ISO or US system.
- Your data never leaves your device
- 100% free
- No sign-up
- Works offline after first load
How to find a week number
- Pick a date — today is filled in.
- Read its week number, the week’s dates and a calendar of that week.
- Switch to “Week → dates” or the US system, or download all weeks of the year.
About Week Number
What week is it? Find the week number of any date in the ISO or US system, the dates of any week number, and every week of the year with its start and end dates.. It works in your browser, so it is instant and private.
Everything you set is remembered on your device, and the result can be copied, shared or printed. The page works offline after the first visit.
Good for
- Planning sprints, shifts and school terms
- Reporting by calendar week
- Logistics and production schedules
Tip: Use “Week → dates” to turn a week number in an email (like KW 42 or W42) into actual dates.
Frequently asked questions
What is the ISO week number?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year’s first Thursday (equivalently, 4 January). It is used across Europe, India and in most business software.
Why do some years have 53 weeks?
An ISO year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year — like 2026. The converter shows how many weeks the chosen year has.
How is the US week number different?
In the US system weeks start on Sunday and week 1 is the week containing 1 January, so the numbers can differ by one from ISO weeks. Switch the week system to compare.
Can I find the dates of a week number?
Yes — choose “Week → dates”, enter the year and week, and you get the Monday-to-Sunday (or Sunday-to-Saturday) dates and a calendar.
Can I see every week of the year?
Yes — the table lists all weeks with their start and end dates; download it as CSV for a planner or spreadsheet.