How to Calculate Percentages in Excel

Calculating percentages trips people up in Excel, usually because of confusion about formatting and formula order. Once you know the patterns, all the common percentage calculations are simple. Here are the ones you'll actually use.

Percentage of a total

To find what percentage one number is of another:

=part / total

Example — 45 out of 180:

=A1/B1

Then format the cell as a percentage (Home > the % button, or Ctrl+Shift+5). The formatting is key: 45/180 gives 0.25, and percentage formatting displays it as 25%. Don't multiply by 100 yourself — the percentage format does that.

Percentage change (increase or decrease)

This is the most-searched percentage calculation. To find the percent change from an old value to a new one:

=(new - old) / old

Example — sales went from 200 (A1) to 250 (B1):

=(B1-A1)/A1

This gives 0.25, formatted as 25% — a 25% increase. If the result is negative, it's a decrease. This single formula handles both increases and decreases; the sign tells you which.

Why old is the denominator: percentage change is always relative to the starting value. Dividing by the old number is what makes it a change, not just a ratio.

Increasing a number by a percentage

To add a percentage to a value (like adding 10% tax or a markup):

=value * (1 + percentage)

Example — increase 200 by 10%:

=A1 * 1.1

The 1.1 means "100% of the original plus 10% more." For 25%, use 1.25; for 5%, use 1.05.

If the percentage is in a cell (say C1 holds 0.10):

=A1 * (1 + C1)

Decreasing a number by a percentage

Same idea, subtracting:

=value * (1 - percentage)

Example — apply a 20% discount to 200:

=A1 * 0.8

The 0.8 means "80% of the original" — a 20% reduction.

Finding the original before a percentage change

If you have a final price that includes, say, 10% tax and want the pre-tax amount:

=final / (1 + percentage)

Example — 220 includes 10% tax; the original was:

=A1 / 1.1

This reverses an increase. It's a common need and easy to get wrong by subtracting 10% instead (which gives a different, incorrect number).

The formatting gotcha

The single most common percentage mistake: confusing the value with its display. In Excel, 25% is the number 0.25 — they're the same value, just formatted differently. So:

• Don't multiply your part/total result by 100 if you're using percentage formatting; you'll get 2500%.
• When typing a percentage into a formula, either type 0.1 or 10% — both work — but not 10 (which means 1000%).

The takeaway

The percentage formulas you'll use most: part/total for a proportion, (new-old)/old for percentage change, value*(1+pct) to increase, and value*(1-pct) to decrease. Format result cells as percentages rather than multiplying by 100 yourself, and remember that in Excel a percentage is just a decimal wearing a % format.