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Percentage calculator

Free · runs in your browser · updated 2026-07-05

To find a percentage of a number, multiply the number by the percentage and divide by 100 — so 15% of 80 is 80 × 15 ÷ 100 = 12. This page also calculates what percent X is of Y, and the percentage change between two numbers.

How to use the percentage calculator

  1. Pick the questionPercent of a number, X as a percent of Y, or percentage change.
  2. Enter the two numbersThe labels update to match the question.
  3. Read the resultThe working is shown so you can repeat it by hand.

Frequently asked questions

How do I work out a percentage without a calculator?

Find 10% by moving the decimal one place left, then scale: 10% of 340 is 34, so 5% is 17 and 15% is 51. For 1%, move the decimal two places.

How do I calculate percentage increase?

Subtract the old value from the new, divide by the old value, then multiply by 100. Going from 250 to 300 is (300−250)÷250×100 = 20% increase.

What's a reverse percentage?

Finding the original value before a percentage was applied. If a price is £60 after a 20% discount, divide by 0.8 to get the original £75 — you can't just add 20% back.

Why is percentage change different in each direction?

Because the base changes. A rise from 100 to 150 is +50%, but the fall from 150 back to 100 is −33%, since it's measured against 150.

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