Knowing the week number—its position from the first week of the year—is vital in many operations. By default, Outlook doesn’t display week numbers, but that doesn’t mean it isn’t possible, and you don’t need code or an add-in.

See more here:
Show week numbers in Outlook’s Calendar

Knowing the week number—its position from the first week of the year—is vital in many operations. By default, Outlook doesn’t display week numbers, but that doesn’t mean it isn’t possible, and you don’t need code or an add-in

The rest is here:
Show week numbers in Outlook’s Calendar