How do I calculate percentage change?

Subtract the old value from the new one, divide by the old value, then multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25 per cent.

How do I remove VAT or sales tax from a total?

Divide by one plus the rate, not by subtracting the percentage. At 20 per cent, the net of 120 is 120 ÷ 1.2 = 100, not 120 − 24 = 96.

Do two discounts add up?

No. Each applies to the reduced price, so 20 per cent then a further 20 per cent gives 36 per cent off in total, not 40.

Percentage Calculator

Quick answer

A percentage of a number is the percentage divided by 100, multiplied by the number. 15% of 240 is 0.15 × 240 = 36.

Percentage of a number

Also shows the value increased and decreased by that percentage.

Percentage (%)

Of this number

Result

36.00

percent% of value

Increased by that %

276.00

Decreased by that %

204.00

Percentages are the arithmetic people most often get subtly wrong, usually because two different questions sound almost identical. "What is 20% of 80" and "20 is what percent of 80" have different answers — 16 and 25 — and the wording rarely makes clear which one is meant.

The other common trap is direction. Adding a percentage and then removing the same percentage does not bring you back where you started, and the gap grows quickly with the size of the percentage.

Why a 50% rise then a 50% fall leaves you down 25%

Each percentage is applied to whatever the number currently is, not to the original. Raise 100 by 50 per cent and you have 150; cut 150 by 50 per cent and you have 75, a quarter below where you started.

This is why a share that falls 50 per cent needs to rise 100 per cent to recover, and why a discount stacked on a discount is never the sum of the two. Two consecutive 20 per cent reductions give 36 per cent off, not 40.

Percentage points are not percentages

If an interest rate moves from 4 per cent to 5 per cent, that is a rise of one percentage point — but a rise of 25 per cent in relative terms. Reporting that mixes the two is how the same change gets described as both small and dramatic.

When you read a claim about a change in any rate, check which of the two is meant. The relative figure is almost always the larger and more persuasive number, which is why it tends to be the one quoted.

Frequently asked questions

How do I calculate percentage change?: Subtract the old value from the new one, divide by the old value, then multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25 per cent.
How do I remove VAT or sales tax from a total?: Divide by one plus the rate, not by subtracting the percentage. At 20 per cent, the net of 120 is 120 ÷ 1.2 = 100, not 120 − 24 = 96.
Do two discounts add up?: No. Each applies to the reduced price, so 20 per cent then a further 20 per cent gives 36 per cent off in total, not 40.

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Updated 2026-09-20 · all calculators. Results are estimates for guidance, not professional advice.