ISO Week Number
DATES & TIME
ISO Week Number
Find the ISO week and ISO week-year.
UNDERSTAND YOUR RESULT
How it works
Find the ISO week and ISO week-year.
THE CALCULATIONweeks start Monday; week 1 contains January 4
Using this calculator
Enter date. weeks start Monday; week 1 contains January 4.
What to keep in mind
Gregorian calendar, years 1900–9999. Calendar dates use UTC to avoid daylight-saving shifts. Business days mean Monday–Friday; holidays are not excluded.
Frequently asked questions
Are my entries saved?
No. Calculator inputs remain in the current page and are cleared when you reload or leave. The tools do not upload your entries.
Why are results rounded?
The display is rounded for readability. Calculations use unrounded intermediate values. An estimate should not be interpreted as an exact measurement.