Week Number Calculator
Find the ISO week number for any date. See which dates are in any given week number. Useful for work planning and scheduling.
How to use
ISO week numbers
ISO 8601 week numbers run Monday to Sunday. Week 1 is the week containing the first Thursday of the year. Some years have 53 weeks. Week numbers are widely used in European business, project management and manufacturing scheduling.
Week to dates
Switch to "Week number → Dates" to find all the dates in any given week number. Enter a year and week number to see Monday through Sunday of that week — useful for scheduling across week boundaries.
Frequently asked questions
Is the Week Number free to use?
Yes, the Week Number is completely free. There is no sign-up, no account required, and no limit on how often you can use it.
Does the Week Number use my time zone?
Yes, the Week Number uses your device's local time zone by default. You can also work with dates explicitly without time zone effects where applicable.
What devices does the Week Number work on?
The Week Number works on any device with a modern web browser — desktop, laptop, tablet, or phone. It is mobile-friendly and works offline once the page has loaded.