Excel formula displays formula rather than result

Edit your formula and be sure there isn't a ' before the = sign.

The cell may have been formatted as text before the formula was entered. Select the cell, then right-click and select Format Cells. Format the cell as General (on the Number tab), then click OK. Press F2, then Enter.

Another possibility is that you have accidentally toggled the view to display formulas rather than their results. Pressing Ctrl + ` (backtick, found next to the left of the number 1 on US keyboards) to toggle the view back to normal