Tool capabilities
- Input
- Options
- Output
- Options
How to use ISO Week Number
Find the ISO week number and week year. This iso week number works directly in your browser and is free to use without an account.
- Choose the date, time zone or calendar values in the fields.
- Read the result and adjust the input to compare another date.
- Copy the value into your own document or code.
ISO Week Number · Example
Input
2021-01-01
Output
2020-W53
The ISO week year can differ from the calendar year.
Usage notes
Inputs and results are processed on this device. Tool content is not sent to a processing server.
Calendar arithmetic uses UTC dates to avoid daylight-saving shifts. Live world clocks use the device clock and the browser time-zone database.