ISO week calendar

Find the ISO week-year, week number and Monday-to-Sunday dates.

Your input

Outputs are cleared when the input changes.

Result

Enter your data or use the example, then run the tool.

Worked example

2021-01-01 belongs to 2020-W53; 2021-01-04 begins 2021-W01.

Method

Use UTC calendar days. The week containing January 4 or the first Thursday is week one.

Limits

Dates 1900–2100; week-year may differ from calendar year. No Sunday-first or IP-zone reinterpretation.

Sources

ISO 8601 date and time format

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