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OS Authority

Calculate percentage increase and decrease

See by how much a price, salary or score went up or down in percent, or what a value becomes after a percentage increase or discount.

Calculations run on this device. We don't see, store or log the numbers or dates you enter.

How it works

  1. Type the old value and the new value to see the percentage change.
  2. Or type a value and a percentage to see it increased and decreased.
  3. Read the answer below the fields, or tap Copy.

The formula

Percentage change = (new − old) ÷ old × 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. From 100 to 80: (80 − 100) ÷ 100 × 100 = 20% decrease. The same difference of 20 is a different percentage, because it is measured against a different starting value.

Increasing or decreasing by a percentage

To add 15% to 200, multiply by 1.15: 230. To take 15% off 200, multiply by 0.85: 170. A 50% increase followed by a 50% decrease does not bring you back: 100 → 150 → 75.

Percentage vs percentage points

If an interest rate moves from 4% to 5%, it rose by 1 percentage point, which is a 25% increase. Use percentage points for differences between two percentages.

Frequently asked questions

What if the old value is 0?

A change from 0 has no percentage: any increase from zero is infinitely large, so the calculator shows no result.

How is a change between negative numbers handled?

It is measured against the size of the starting value: from −50 to −100 is a 100% decrease.

How do I reverse a discount?

Divide by the remaining share: a price of 85 after a 15% discount was 85 ÷ 0.85 = 100.

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