WEEKNUM Function in Excel: Week Number of the Year

⏱ 1 min readUpdated 28 September 2026

Date & TimeLevel: IntermediateAvailable in: Excel 2007+

In this article
  1. Syntax
  2. Examples
  3. Example 1
  4. Example 2
  5. Common errors and fixes
  6. Related functions

WEEKNUM returns the week of the year. ISOWEEKNUM follows the ISO standard (weeks start Monday, week 1 contains the first Thursday).

Syntax

=WEEKNUM(serial_number, [return_type])
Argument What it means
return_type 1 (default) weeks start Sunday; 2 start Monday; 21 = ISO.

Examples

Example 1

=WEEKNUM(A2, 2)

Monday-based week number for weekly sales reports.

Example 2

=ISOWEEKNUM(A2)

The week number most European/global companies use.

Common errors and fixes

You see Why, and the fix
Numbers differ from a colleague Different return_type. Agree on one (2 or ISO) across the team.

WEEKDAY · TEXT

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