The SUM function totals a series of numbers. It takes the form =SUM(number1, number2, …). The number arguments are a series of as many as 30 entries that can be numbers, formulas, ranges, or cell references that result in numbers. SUM ignores arguments that refer to text values, logical values, or blank cells. The AutoSum Button

Because SUM is such a commonly used function, Excel provides the AutoSum button on the Standard toolbar. If you select a cell and click the AutoSum button, Excel creates a SUM formula and guesses which cells you want to total. To enter SUM formulas into a range of cells, select the cells before clicking AutoSum.

Automatic Range Expansion

Ever since the first spreadsheet program was created, one of the most common problems has been inserting cells at the bottom or to the right of a range that is already referenced in a formula. For example, suppose you type the formula =SUM(A1:A4) in cell A5, and then select row 5 and insert a new row. The new row is inserted above the selected row, thus pushing the SUM formula down to cell A6. Any numbers in the new inserted cell A5 are not included in the SUM formula.

A few versions ago, Excel changed all that. Now you can insert cells at the bottom or to the right of a range referenced by a formula, and Excel adjusts the formulas for you—and this is key—as soon as you type values in the new inserted cells.

This works only when you insert cells immediately to the right or below a referenced range. Inserting cells at the top or to the left of a referenced range still involves editing the referencing formulas manually.