This FAQ covers 3 common question types about WEEKNUM, including formula errors, different week-number results, and date recognition issues.
FAQ
What should I do if the WEEKNUM function shows an error?
- Check whether the formula starts with
=. - Make sure the parentheses are paired correctly and the arguments use the correct separator.
- Confirm that the date argument is a valid date, a cell reference to a date, or a formula that returns a date.
- If you entered a second argument, make sure its value matches the function rule you want to use.
Why can the same date return different week numbers?
- Check whether the WEEKNUM formula uses a second argument.
- Confirm which week-start rule is currently being used.
- If you need ISO week numbering, use the corresponding parameter setting before comparing results.
- Keep the parameter pattern consistent across the worksheet so one column does not mix different rules.
Why is the WEEKNUM result not updating automatically?
- Make sure the referenced date cell has been edited and the input is confirmed.
- Check whether the formula points to the correct cell.
- Review whether the date cell contains text instead of a real date value.
- Confirm the formula again and press Enter so the worksheet recalculates the current result.
Glossary
| Term | Definition |
|---|---|
| WEEKNUM | A date function that returns which week of the year a specified date belongs to. |
| Date argument | The input value used in WEEKNUM to specify the target date, such as a date, a cell reference, or a formula that returns a date. |
| Week start day | The rule that defines which day starts a week, which can affect the returned week number. |