Free week number calculator
Week Number Calculator
Calculate the ISO week number, ISO week-year, weekday number, and weeks in the year.
Developer utility
Browser based
Runs on the current page
Copy-ready
Use the output where you work
No sign-in
Open the tool and get moving
Date tool
Week Number Calculator
Find the ISO week number, week-year, weekday number, and day of year for any date.
ISO week
Week 32
ISO week-year
2026
ISO weekday
2
Monday is 1, Sunday is 7
Weeks in year
53
ISO weeks start on Monday. Week 1 is the week containing the first Thursday of the year.
Built for developers
Small utilities for fast technical checks.
Entwicklera developer tools are made for everyday formatting, encoding, decoding, generation, and inspection tasks during implementation and debugging.
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FAQ
Week Number Calculator questions.
When does an ISO week start?
ISO weeks start on Monday. Week 1 is the week that contains the first Thursday of the year.
Why can the ISO week-year differ from the calendar year?
Dates near January 1 or December 31 can belong to the previous or next ISO week-year depending on how that week falls.
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