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Inputs remain on your device.
ISO Week Calculator
Find the ISO week, day of year, quarter and remaining ISO weeks.
Calculations happen locally; dates and time zones are not transmitted.
How to use the iso week calculator
- 1
Enter the required dates, times or options.
- 2
Select Calculate to run the operation locally.
- 3
Review and copy each format or print the result.
Calendar accuracy in your browser
Explicit rules
Validates ranges, leap years and month changes.
International formats
Uses Intl and IANA to localize results.
Frequently asked questions
What is an ISO week?
ISO weeks start Monday and week 1 is the week containing the year's first Thursday.
Are my dates sent to a server?
No. Every operation runs in your browser.
Which calendar is used?
It uses the Gregorian calendar and dates from years 1 through 9999.