WEEKNUM function
Quick answer
WEEKNUM returns the week number of a date in its year, 1 to 54.
- Syntax
=WEEKNUM(serial_number, [return_type])- Most common use
=WEEKNUM(A2)returns 1 (January 1 is always week 1 in the default system)
By default weeks start on Sunday and the week with January 1 is week 1; return_type 2 starts weeks on Monday, and 21 gives ISO week numbers. Use it to group dates by week in reports, summaries and charts.
- Available in
- Every current version
- Category
- Date functions
- Returns
- A whole number from 1 to 54.
- Google Sheets
- Works the same in Google Sheets.
Syntax
=WEEKNUM(serial_number, [return_type])
| Argument | Required? | What it is |
|---|---|---|
serial_number | Required | The date. |
return_type | Optional | Optional: 1 or omitted, weeks start Sunday; 2 or 11, Monday; 12–17, Tuesday to Sunday; 21, ISO weeks. |
Examples
Each result below is calculated from the sample sheet by our formula engine, the same one that grades the practice.
| Cell | Formula | Result | What it shows |
|---|---|---|---|
| B2 | =WEEKNUM(A2) | 1 | January 1 is always week 1 in the default system |
| B3 | =WEEKNUM(A3,2) | 11 | Weeks starting Monday: March 9 is in week 11 |
| B4 | =WEEKNUM(A4,21) | 53 | ISO week of December 31, 2026: 53 |
Try it live
This is the sample sheet. Change any number or text, or edit a formula, and the results update.
Show the sample data as a table
| Date | Result |
| 1/1/2026 | 1 |
| 3/9/2026 | 11 |
| 12/31/2026 | 53 |
Practice WEEKNUM
Graded instantly, then re-checked on changed data.
Week of each order
C2, return the week number of each order date in B2, with weeks starting on Monday. Fill down to C7.Common mistakes
| What you see | Why, and how to fix it |
|---|---|
| Week numbers don't match the calendar at work | Your company may use ISO weeks. Use return_type 21, or ISOWEEKNUM. |
| #NUM! | return_type isn't one of 1, 2, 11–17 or 21. |
| Week 53 or 54 | In the default system the last days of December can fall in week 53, or 54 in a leap year that starts on a Saturday. |
Tips
- For weekly totals, add a WEEKNUM column and use it in SUMIFS or a pivot table.
Questions
How do I get the week number of a date in Excel?
=WEEKNUM(A2) for weeks starting Sunday, =WEEKNUM(A2,2) for weeks starting Monday, or =ISOWEEKNUM(A2) for ISO weeks.
What is the difference between WEEKNUM and ISOWEEKNUM?
WEEKNUM's week 1 is the week that contains January 1. ISO week 1 is the week with the year's first Thursday, so early January can be week 52 or 53 of the year before.
Updated Checked by running: every formula on this page was run by our formula engine on .