Numbers 10.1

The most common problem is that the "numbers" you are trying to sum are not actually numbers, they are formatted as text. The math operators (+ - * /) will work on them as if they are numbers but many/most functions will not. Click on one of those "number" cells and look at the bottom left corner of the window. If it says "text", that's the problem. If it says "actual", they are actual numbers.

If they are text, select all of them and change the cell format to a number format using the sidebar on the right (with all the cell formatting stuff). Just to be sure it worked, click off of them then select them again and look again at the format. It should be what you changed it to. If the format reads "multiple", some cells are still wrong because there is something non-numeric in them.

A likely issue, then is that you have no summable values in the set of cells whose content is being summed.

That's a guess, of course, as you have provided NO information on which to base a diagnosis.

Here's a test that may confirm that guess.

Select an empty cell on your table, then press = to open the Formula Editor.

In the formula editor enter these two characters: 1* then click the topmost or leftmost cell containing one of the values that is to be summed. (Note that Numbers will automatically change the * to a multiplication sign.) Then click the green checkmark to confirm the formula and close the inspector.

What result do you see in the cell where you entered the formula?

Also, please provide a copy of your SUM formula and a screen shot of the cells (including the row and column reference tabs for those cells) referenced in that formula.

Regards,

Barry