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Week Number Calculator and Day Information

Find the ISO week number for any date and check useful calendar information including the day of the week, day of the year, and the Monday and Sunday dates for the selected ISO week.

Week Number Calculator

Day Information

Week Number Calculator

The Week Number Calculator helps you find the ISO week number for any selected date. It also shows the ISO week-numbering year, the Monday when that week begins, and the Sunday when the week ends.

The Day Information tool provides additional calendar details for a selected date, including the day of the week, day of the year, and ISO week number. You can use it for current dates as well as supported past and future dates.

Ways to Use the Week Number Calculator

Find the week number

Select any date to find its ISO week number and the corresponding ISO week-numbering year.

Check the current week

Use today's date to quickly determine the current ISO week number.

Find the day of the week

Check whether a past, present, or future date falls on Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday.

Find the day of the year

Calculate the sequential day number of a date, from day 1 on January 1 through day 365 or 366 at the end of the year.

Find the start and end of a week

See the Monday start date and Sunday end date of the ISO week containing your selected date.

Plan schedules by week

Use ISO week numbers when organizing projects, work schedules, school calendars, reports, deadlines, and other week-based plans.

Week Number Calculator Features

  • ISO week number calculation
  • ISO week-numbering year
  • Day of the week
  • Day of the year
  • Monday week start date
  • Sunday week end date
  • Today's date shortcut
  • Past date calculations
  • Future date calculations
  • Leap year support
  • 52 and 53-week year support
  • Browser-based calculation
  • No installation required
  • Responsive layout
  • Light and dark themes

How to Use the Week Number Calculator

  1. 1

    Select a date

    Choose the calendar date you want to check. You can also use the shortcut to enter today's date.

  2. 2

    Calculate the date information

    Use the Day Information calculator to find the weekday, day of the year, and ISO week number for the selected date.

  3. 3

    Check the ISO week

    The ISO week number identifies which numbered week of the ISO week-numbering year contains the selected date.

  4. 4

    View the week boundaries

    Use the Week Number Calculator to see the Monday when the selected ISO week begins and the Sunday when it ends.

ISO Week Number Calculator

Select a date to calculate its ISO week number. ISO week numbering organizes the year into weeks beginning on Monday and is commonly used for schedules, reporting, planning, and week-based calendars.

What Week Is It?

Use today's date to find the current ISO week number. The result also identifies the ISO week-numbering year associated with that week.

Day of Week Calculator

Find which day of the week a specific date falls on. Select a past, present, or future date to check whether it is Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday.

Day of Year Calculator

Find the ordinal day number of a date within its calendar year. January 1 is day 1, while the final date of the year is day 365 in a common year or day 366 in a leap year.

Week Start and End Date Calculator

Find the full ISO week containing a selected date. The calculator shows the Monday at the beginning of the week and the Sunday at the end of the week.

ISO Week Date for Planning

Week numbers can be useful when organizing project schedules, work periods, school calendars, delivery dates, reports, and other activities that are planned by week rather than by individual calendar dates.