Begin every formula with an equal sign (=). The equal sign tells Excel that the string of characters you're entering into a cell is a mathematical formula. If you forget the equal sign, Excel will treat the entry as a character string.

Use coordinate references for cells that contain the values used in your formula. While you can include numeric constants in your formulas, in most cases you'll use values entered in other cells (or the results of other formulas displayed in those cells) in your formulas. You refer to those cells with a coordinate reference of the row and column the cell is in. There are several formats: The most common coordinate reference is to use the letter or letters representing the column followed by the number of the row the cell is in: A1 refers to the cell in Column A, Row 1. If you add rows above the referenced cell or columns above the referenced cell, the cell's reference will change to reflect its new position; adding a row above Cell A1 and a column to its left will change its reference to B2 in any formula the cell is referenced in. A variation of this reference is to make row or column references absolute by preceding them with a dollar sign ($). While the reference name for Cell A1 will change if a row is added above or a column is added in front of it, Cell $A$1