Week Number: instructions, examples and limits
ISO 8601 weeks start Monday.
Open Week NumberThis tool is registered for local processing. Its tool input is handled in the current page; LittleKit’s product analytics do not include the input value.
What it does
ISO 8601 weeks start Monday. Week 1 contains 4 January; the week-year may differ from the calendar year.
Worked example
2021-01-01 → 2020-W53.
The example demonstrates the operation. For file-based tools, results depend on the selected file and options.How the result is produced
ISO 8601 weeks start Monday. Week 1 contains 4 January; the week-year may differ from the calendar year.
Important limits
Date-only calculations use the Gregorian calendar and UTC day boundaries, so daylight-saving changes do not alter day counts. Years 0001–9999.
Choosing the next step
Use a calendar-date tool when the question is about dates on a page, and a duration tool when elapsed clock time matters. For a deadline across time zones, convert the times explicitly before relying on a local-device result.
See a mismatch between these instructions and the tool? Report a correction with a non-sensitive example.