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📅 Day of Week Finder
Find which day of the week any date falls on — plus its day of the year and ISO week number.
About this Day of Week Finder
Day of Week Finder answers 'what day was that?' for any date — past or future — and adds two facts planners love: the day number within the year and the ISO week number used in business calendars. It is perfect for checking birthdays, anniversaries, historical dates and project schedules.
How to use it
- Pick any date in the date box.
- Press Find the day (or just change the date).
- Read the weekday name, day of year and ISO week number.
- Try your birth date to see which weekday you were born on.
Example
1 January 2000 fell on a Saturday — day 1 of the year, in ISO week 52 of 1999.
Frequently asked questions
What is an ISO week number?
It is the week-counting system used in business and logistics, where weeks start on Monday and week 1 contains the year's first Thursday.
How far back or forward does it work?
The calendar math works for any year your browser can represent — centuries in either direction are fine.
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