Weekday and week number
See the day of the week, the ISO week number and the day of the year for any date.
How to find the weekday and week number of a date
Type any date and see what day of the week it falls on, its ISO week number and week year, and which day of the year it is. This is handy for planning around week numbers, which many workplaces in Europe use, for checking a historic date, or for finding the day of the week of a birthday.
Step by step
- Type the date in any format, such as 7/4/2027 or July 4 2027, or pick it from the calendar.
- Press Show weekday and week number.
Worked examples
- ISO weeks: January 1, 2027 is a Friday in week 53 of ISO year 2026. ISO week years can start a few days before or after January 1.
- Leap day: February 29, 2024 was a Thursday, day 60 of 366.
- Year end: December 31, 2026 is a Thursday, day 365 of 365, in ISO week 53.
Common uses
- Week numbers at work. Many European companies plan by week number: "delivery in week 47". Enter a date to find its week, or check which dates a given week covers by trying its Monday.
- What day was it. Find the day of the week of a birth date, a wedding or a historic event. The tool works for any year from 1 to 9999.
- Day of the year. Useful for Julian style day numbers used in manufacturing date codes, logistics and some government forms.
- Planning a date. Check whether a chosen date falls on a weekend before you book or announce it.
Reading the result
The result names the weekday first, then the ISO week and its week year, then the day of the year out of 365 or 366. The calendar shows the whole month with the chosen date marked, so you can see the surrounding weekdays without another lookup.
Handy facts
- A year is a leap year if it divides by 4, except century years, which must divide by 400. So 2000 was a leap year and 2100 will not be.
- A common year has 52 weeks and 1 day. A leap year has 52 weeks and 2 days.
- ISO weeks start on Monday, and week 1 is the week that contains January 4. Some years have 53 ISO weeks.
Questions people ask
Why does the week year differ from the calendar year?
ISO week 1 is the week with the first Thursday of the year, so the last days of December can belong to week 1 of the next year, and the first days of January can belong to week 52 or 53 of the previous one.
Does this use the U.S. week numbering?
No. It uses ISO 8601 week numbers, which start on Monday. Calendars that start weeks on Sunday can show a different number.
How far back does it go?
Years 0001 to 9999 on the Gregorian calendar. Dates before 1582 are shown as if the Gregorian calendar had been in use then, which is how most software works.
Can I find the dates of a given week number?
Enter any date you think is in that week and read the result; then move a day at a time with the arrow keys until the week number changes to find its Monday and Sunday. A week number tool that goes the other way is on our list.
Why is the day of the year different from what my spreadsheet shows?
Most spreadsheets agree with this tool. If yours is off by one, it may be counting from zero or using a different year start. January 1 is day 1 here.
Is my date sent anywhere?
No. The lookup runs in your browser.