Week Number
Find the ISO 8601 week number, day of year, and other calendar facts for any date. Useful for scheduling, reporting, and payroll systems that use week numbers.
ISO Week
Day of Year
Day of Week
Days Left in Year
How to use
- The calculator defaults to today's date and shows results immediately on page load.
- Change the date using the date picker to look up any date in the past or future.
- The ISO week number follows ISO 8601: weeks start on Monday, and week 1 contains the first Thursday of the year.
Frequently asked questions
- Is this week number tool free?
- Yes, completely free with no signup and no usage limits.
- Does it upload any data?
- No. All calculations run in your browser — your dates never leave your device.
- Does it work on mobile?
- Yes. Works in Safari, Chrome, and Firefox on iOS and Android.