Week Number Calculator

How to use

1. 1Pick the week numbering standard at the top: ISO 8601 (Monday start, used in Europe) or US (Sunday start, used in US payroll and retail).
2. 2The Current week panel shows today's week number, day of year, and quarter. The headline updates every minute.
3. 3To look up a different date, edit the date input. The Result panel shows the week number, the start and end of that week, weekday, and quarter. Use Today, +1 week, -1 week, or the day arrows for quick navigation.
4. 4To go from week number to dates, fill in the Year and Week number fields. The page returns the Monday and Sunday (ISO) or Sunday and Saturday (US) of that week.
5. 5Open the Year overview table to see every week of any year with its start and end dates. Use Copy summary or Copy range to grab the current result.

About this tool

Week Number Calculator answers the everyday "what week is it?" question against the two real-world week-numbering conventions used in business and software. Pick a numbering standard at the top of the page and the rest of the tool follows it. The ISO 8601 standard, used in Europe and by most calendar libraries, places week 1 on the week containing the first Thursday of the year and starts each week on Monday; under ISO 8601 some Januaries belong to week 52 or 53 of the previous ISO year, and some Decembers belong to week 1 of the next. The US convention, common in payroll, retail, and broadcast, places week 1 on January 1 regardless of weekday and starts each week on Sunday. Use the page to read the current week number for today (the headline ticks every minute so it stays accurate without refreshing), look up any date in the past or future to see its week number plus the start and end dates of that week, see the day of year, current quarter, weekday, and total weeks in the year (52 or 53), or work the other direction with a Week-number-to-date converter that takes a year and a week number and returns the Monday and Sunday of that week. A year overview table lists every week of the chosen year with its start and end date, with the current week highlighted when the overview year matches today. Useful for project managers planning sprints by ISO week, retail and supply teams tracking weekly KPIs, payroll teams running weekly cycles, freight and logistics teams referencing carrier week numbers, students and academics handling syllabus weeks, and anyone who needs to translate between calendar dates and week numbers. All math runs locally in your browser; no dates are uploaded.

Free to use. Works in your browser. No signup, no login.