WEEKNUM Function in Excel: Week Number of the Year

📎 This article includes 1 downloadable practice file ↓

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. WEEKNUM in practice
7. Where you will use it
8. Worked example
9. Mistakes people make
10. Related functions
11. Continue learning

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.

WEEKNUM in practice

Where you will use it

• Weekly sales reports
• Week of the year for planning
• Group dates by week

Worked example

Date	Formula	Result
01-Jan-2026	=WEEKNUM(A2,2)	1
04-Oct-2026	=WEEKNUM(A3,2)	40
31-Dec-2026	=WEEKNUM(A4,2)	53

Results calculated in Excel.

Mistakes people make

Mistake	What to do instead
Week start	Type 2 starts weeks on Monday
ISO weeks	Use ISOWEEKNUM for ISO 8601

Related functions

WEEKDAY · TEXT

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📎 Practice files for this article

• 📗
  Practice workbook: Dates & times22 tasks on realistic sales data — type your formula, the Check column turns green when it is right. Answers sheet included.
  ⬇ XLSX · 34 KB

Free to use for learning. Files with macros (.bas) are plain text — import them with Alt+F11 → File → Import File, and always test on a copy.