Percentage Increase and Decrease Calculator
Add or take away a percentage from any number.
Good to know. A 20% raise followed by a 20% cut leaves you 4% worse off. The order doesn’t save you.
How it works
In plain words
Turn the percentage into a multiplier: 1 plus the percentage for an increase, 1 minus it for a decrease. Then multiply the starting value by it.
The formula
increase: new = value × (1 + p ÷ 100) decrease: new = value × (1 − p ÷ 100)
Worked example
A 5% rise on 2,500: the multiplier is 1.05, and 2,500 × 1.05 = 2,625. The change is 125.
Sources
No outside data or rates: this is plain arithmetic.
7 automated tests check its answers on every change.
About the percentage increase and decrease calculator
This calculator answers "what is X plus 5%?" or "what is X minus 12%?" in one step. It is the calculation behind pay rises, price increases, rent adjustments, and cutting a budget by a set percentage.
The trick is to think in multipliers. A 5% increase means you keep 100% of the original and add 5%, so you multiply by 1.05. A 12% decrease means you keep 88%, so you multiply by 0.88. This is faster than working out the percentage and adding or subtracting it, and it is how spreadsheets and accountants do it.
Multipliers also explain why repeated changes don’t simply add up. Two 10% increases are 1.1 × 1.1 = 1.21, a 21% total rise, not 20%. A 10% increase followed by a 10% decrease leaves you at 0.99, slightly below where you started.
A decrease of more than 100% gives a negative result, which rarely makes sense for prices but can be meaningful for things like profits. If you have the new value and want to find the original, use the reverse percentage calculator instead.
Questions people ask
How do I add 5% to a number?
Multiply it by 1.05. For 2,500 that gives 2,625.
How do I take 20% off a number?
Multiply it by 0.8. For 150 that gives 120.
If something rises 10% then falls 10%, is it back where it started?
No. 100 rises to 110, and 10% of 110 is 11, so it falls to 99. The second change is based on a bigger number.
How do I undo a percentage increase?
Divide by the multiplier instead of subtracting the percentage. To remove a 5% rise from 2,625, divide by 1.05 to get 2,500. The reverse percentage calculator does this for you.