How to Calculate Percentages in Excel

Setting up percentage formatting

Excel has a dedicated percent format. Select cells, click the % button in the Number group, or press Ctrl+Shift+5. Once formatted, typing 0.15 displays as 15%. Excel stores the underlying value as 0.15 — the percent sign is purely cosmetic.

Formula 1: percentage of a number

To compute 15% of a value in cell A1:

=A1*0.15

Or, more readably:

=A1*15%

Both give the same result. Excel parses 15% as 0.15 in formulas.

Formula 2: what percent is X of Y

If A1 holds the part (12) and B1 holds the whole (80):

=A1/B1

Format the cell as percent. The displayed result is 15%; the underlying value is 0.15.

Formula 3: percentage change between two values

Old value in A1, new value in B1:

=(B1-A1)/A1

A positive result is an increase; negative is a decrease. Format as percent.

Formula 4: percent of total in a column

If you have values in A2:A20 and want each row’s share of the total:

=A2/SUM($A$2:$A$20)

The $ signs lock the total range when you drag the formula down.

Common Excel percentage gotchas

• Typing 15 in a percent-formatted cell stores 15 (1500%), not 0.15. Type 0.15 or 15% instead.
• Multiplying two percent-formatted cells works numerically but can be confusing. 20% × 30% = 6%, not 50%.
• Negative percent change with old value = 0 produces #DIV/0!. Wrap in IFERROR().