What Week Is It? Week Number Today and Calendar

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Find the week number for today or any date. The tool shows the ISO 8601 week used in Europe, Asia and most business calendars, where weeks start on Monday, plus the US-style week number that starts on Sunday, and a full list of every week in the year with its dates.

–ISO week
–US week (Sunday start)
–Day of year
–ISO weeks this year
WeekMondaySunday

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Quick answer: The big number at the top is the current ISO week. ISO weeks start on Monday, and week 1 is the week that contains the first Thursday of January, so a year has 52 or 53 weeks.

How to find the week number

  1. The tool opens on today’s date and shows this week’s number straight away.
  2. Pick any other date to get its ISO week, its US week number and its day of the year.
  3. Change the year to list every week with its Monday and Sunday dates. The current week is highlighted.

ISO week numbers explained

The ISO 8601 standard is used across Europe, in much of Asia and in most planning, payroll and manufacturing software. Its rules are simple:

  • Weeks start on Monday and end on Sunday.
  • Week 1 is the week with the year’s first Thursday in it, which is the same as the week that contains January 4.
  • Most years have 52 weeks. Years that start on a Thursday, and leap years that start on a Wednesday, have 53.
  • Because of this, January 1 to 3 can belong to the last week of the previous year, and December 29 to 31 can be in week 1 of the next year.

ISO weeks are written like 2026-W42, or with a day number, such as 2026-W42-3 for the Wednesday.

US week numbers

Calendars in the United States, Canada and some other countries usually start weeks on Sunday and call the week containing January 1 “week 1”. That can give a number one higher than the ISO week. Outlook, Google Calendar and Excel can show either system, so check which one your team uses.

Week numbers in Excel and Google Sheets

Use =ISOWEEKNUM(A1) for the ISO week, or =WEEKNUM(A1) for the US-style week starting on Sunday. In Google Sheets, =WEEKNUM(A1, 21) also returns the ISO week.

More date tools: find the weekday of any date with the day of the week calculator, count the gap between two dates with days between dates, or count down to an event with the countdown timer.

FAQ

What week of the year is it?

The number at the top of the tool is today’s ISO week, based on your device’s date.

How many weeks are in a year?

52 weeks and 1 day, or 52 weeks and 2 days in a leap year. In ISO terms a year has either 52 or 53 numbered weeks.

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