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
Find the ISO 8601 week number for any date. ISO weeks start on Monday, and the first week of the year is the one containing its first Thursday, so week numbers can differ from other systems. It runs 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.