Error ExplainerExcel #NUM! error
A plain-words explanation of this Excel message: what it means, the usual causes, and the steps that fix it.
The message#NUM!
Make the error yourself
Typed into Microsoft Excel 16.0 build 20326. This is the smallest example we could find that shows it.
| Cell | What was typed |
|---|---|
| A1 | -4 |
| B1 | =SQRT(A1) |
The cell looked at: B1.
Excel shows: #NUM!
Why it happens
#NUM! means a number is not acceptable for the function or the result is too large or too small for Excel. The example takes the square root of a negative number, which has no real answer. Other causes: functions that find an answer by repeated trials (IRR, RATE, XIRR) and cannot find one, numbers beyond about 1E+308, LARGE or SMALL asked for a position that does not exist, and a date outside the range that Excel supports.
How to fix it
- Check the arguments of the function: do negative numbers, zero or very large numbers make the function impossible?
- Test them first:
IF(A1<0, "...", SQRT(A1))orSQRT(ABS(A1))if the sign does not matter. - For
IRRandRATE, give a guess value as the last argument, and check that the cash flows have at least one positive and one negative number. - Make sure that dates and times are real dates, not text.
The corrected version
| Cell | What was typed |
|---|---|
| A1 | -4 |
| B1 | =IF(A1<0,"negative number",SQRT(A1)) |
The cell looked at: B1.
Excel shows: negative number
How to avoid it
Validate inputs for functions that have a limited range, and give iterative functions a good starting guess.
Questions
Why does IRR give #NUM!?
Excel tries up to a set number of times to find a rate. If the cash flows have only positive or only negative values, no rate exists.
This is an independent guide. It is not connected with Python, Microsoft, Google, GitHub or the Git project. Product names belong to their owners. Examples were run on 13 November 2026 in a practice folder or a blank workbook; your version may word a message slightly differently.