Percentage Decrease Calculator

Multiply by what is left

new = old × (1 − percentage ÷ 100)

To take 15 % off, multiply by 0.85 — because 85 % is what remains. To halve something, multiply by 0.5. It is one step rather than two.

Down and back up is not a round trip

Take 20 % off 100 and you get 80. Add 20 % back and you get 96, not 100.

The reason is the baseline. The 20 % coming off was 20 % of 100; the 20 % going back on was 20 % of 80, which is only 16. Bigger percentages make the gap wider: down 50 % and up 50 % leaves you at 75.

To actually undo a decrease you divide rather than multiply, which is what the reverse percentage calculator does.

Stacked discounts do not add up

A shop advertising "30 % off, then a further 20 % off" is not offering 50 % off. It is 0.7 × 0.8 = 0.56, so 44 % off. The second discount applies to the already-reduced price.

Common uses

• Sale prices — and stacked offers, where the arithmetic favours the shop.
• Depreciation year on year.
• Removing a markup or a commission.
• Budget cuts expressed as a percentage.

The working, step by step

Questions people ask

How do I decrease a number by a percentage?

Multiply by 1 minus the percentage as a decimal. To take 15 % off, multiply by 0.85.

Why does adding the percentage back not restore the original?

Because the second percentage applies to the reduced number. Down 20 % then up 20 % leaves you 4 % short.

Is 30% off then 20% off the same as 50% off?

No. It works out at 44 % off, because the second discount applies to the already-reduced price.

Nothing here is sent anywhere

The arithmetic happens in your browser as you type. The numbers you enter are not transmitted, logged or stored, because the page has no server behind it to receive them.