Week Number Lookup
9 toolsFind the ISO 8601 week number for any date.
Runs in your browser — your files and text stay on your device
A complete date and time toolkit — convert Unix timestamps, calculate exact age or the difference between two dates, check the world clock across timezones, run a countdown or stopwatch, add business days, or look up a week number. Everything runs locally in your browser.
Timestamp ConverterAge CalculatorDate DifferenceTimezone ConverterWorld ClockCountdown TimerStopwatchBusiness Days CalculatorWeek Number Lookup
Pick a date
How to use this tool
- 1Pick any date.
- 2Its ISO 8601 week number (and week-year) appears automatically.
Frequently asked questions
What week-numbering standard is this?
ISO 8601 — weeks start on Monday, and week 1 is the week containing the year's first Thursday.
Why does the week-year sometimes differ from the calendar year?
Late-December or early-January dates can belong to a week numbered in the adjacent year under ISO 8601 — this is expected, standard behavior.