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ISO week number
Find ISO week-year, week number and weekday (Monday=1, Sunday=7).
ISO weeks start on Monday, and week one is the week containing January 4. For 2021-01-01, the output is ISO year 2020, week 53 and weekday 5, even though the calendar year is 2021.
How to use
- Enter your text, values, or image.
- Adjust the options and run the tool.
- Copy or download your result.
Worked example
Example input
Date: 2021-01-01
Example result
{
"isoYear": 2020,
"week": 53,
"weekday": 5
}Limitations and details
Input must be a valid Gregorian date in years 0001–9999; ISO week numbering can differ from local or Sunday-first week systems.
Inputs and options
- Date
- Date
Frequently asked questions
Is this tool free and private?
Yes. All 300 tools are free in this phase. Processing happens in your browser; your input and files are not sent to our servers.