Excel "=SUM" formula does not add up numbers correctly

Marsha wrote:

I discovered that, although I had selected cells and formatted them as Number, Excel still had them as General so they were not being counted in the SUM formula. There was a tiny yellow diamond with ! inside next to each one. When I hovered over the diamond and clicked, I was given a menu from which I chose "convert to a number". Problem solved.

The problem was not the cell format; any numeric cell format will do, including General.

The problem was:  the cell value was text, not numeric.  That is the type of the value, not the cell format.

How that happened is anyone's guess.  You offer no clues.  Most commonly, it was the result of copy-and-paste.  Sometimes it is the result of importing from another application.

We can enter text into any cell, regardless of the cell format.  In particular, the cell format does not have to be General or Text.

PS....  Simply changing the cell format is not sufficient to convert the cell value from text to numeric.  We must also "re-enter" the cell value.  That can be done after changing the cell format by selecting each cell and pressing F2, then Enter.  But of course, that is tedious if you have a lot of cells to convert.  There are alternatives, like the one you discovered.  But they all run the risk of changing the cell value infinitesimally in some situations.

For each of those cells that make up the sum, can you select each one at a time and look in the formula bar to see that they actually have 3,001.53 as their value?

I had the same problem in Excel 2013; just about pulled out my hair. I discovered that, although I had selected cells and formatted them as Number, Excel still had them as General so they were not being counted in the SUM formula. There was a tiny yellow diamond with ! inside next to each one. When I hovered over the diamond and clicked, I was given a menu from which I chose "convert to a number". Problem solved.

I had this problem too. Go to Options menu under the File Tab.

Under Excel options there should be one that says Formulas and under that/beside that Calculation Options and Workbook Calculation. Make sure Automatic is checked.

@zardoz2525, check on the bottom left of the status bar to see if you have a circular reference.  Your sheet will not calculate as you would expect until you fix that, however you choose to.