Delivery is scheduled for 11/18/2025, but your client refers to it as week 47. Use WEEKNUM to convert your dates into their planning terminology.

Whether you are preparing a reverse schedule, a project follow–up or an editorial calendar, speaking in weeks allows you to gain clarity… provided you know how to calculate them!

Find the week number in Excel

WEEKNUM allows you to know the week number from a date. It is written as follows:

=WEEKNUM(serial_number, [return_type])

Serial Number: Select the cell containing the date.

Return type: The first 2 options are the most common options.

  • 1: The week starts with Sunday (default option if not specified) = American system
  • 2: The week starts with Monday = European system

But you can start the week on any day by choosing another option.

So, thanks to this feature, we know that 11/18/2025 is in week 47.

View the week number in the Outlook calendar

You can also view week numbers in your Outlook calendar, so you can keep track of different deadlines.

To do this, go to Outlook options. In the Calendar category, go to the Display Options section and check Show week numbers in the month view and the Date Navigator.

When you view your calendar in months, the week number is displayed on the left.

And why not display the holidays in your country and those of the countries you work with in your calendar? This will allow you to synchronize the work on working days! Outlook: Show holidays in the calendar

You are now ready for retroplanning, project follow–ups or exchanges with teams that talk in week numbers!