Week Number & Day of the Week Finder
Find the ISO week number, day of the week, day of the year and quarter for any date — and the dates of any week number.
How to use
- 1Pick a date (or leave empty for today).
- 2Or enter a year and week number to see that week's Monday-to-Sunday dates.
How it's calculated
ISO 8601: weeks start on Monday, and week 1 is the week containing the year's first Thursday (so 29 Dec–3 Jan can belong to either year).
Frequently asked questions
Why is 1 January sometimes in week 52 or 53?
Under ISO 8601, the first week of a year is the one with the first Thursday, so early January days can belong to the previous year's last week.
Do the US and Europe number weeks the same way?
Not always. Europe uses ISO weeks (Monday start). Many US calendars start weeks on Sunday and call the week containing 1 January week 1.
How many weeks are in a year?
52, or 53 in 'long' ISO years such as 2020 and 2026.