Percentage Change Calculator

How it works

Percentage change = (new − old) ÷ |old| × 100. The reverse change is measured from the new value back to the old one. Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100.

How to calculate percentage change

1. Subtract the old value from the new value.
2. Divide by the old value.
3. Multiply by 100. A positive answer is an increase; a negative one is a decrease.

Why an increase and a decrease are not symmetric

Going from 80 to 100 is a 25% increase, but going from 100 back to 80 is only a 20% decrease, because each change is measured against a different starting value. That is why the calculator also shows the reverse change. A 50% loss needs a 100% gain to recover; a 20% loss needs a 25% gain.

Percentage change vs percentage difference

Percentage change has a direction: it compares a new value with an old one. Percentage difference compares two values with no “before” and “after” — two prices in different shops, two measurements — and divides the gap by their average: |A − B| ÷ ((A + B) ÷ 2) × 100. For 80 and 100 the difference is 22.22%. Use percentage change for growth over time and percentage difference for side-by-side comparisons.

Common uses

Salary rises, rent and price increases, stock and sales growth, weight change, website traffic, test-score improvement and inflation are all percentage changes. Year-over-year (YoY) growth compares a value with the same period a year earlier; month-over-month (MoM) compares consecutive months. To find a percentage of a single number instead, use the percentage calculator.