Reverse Percentage Calculator
Recover the original number when all you know is the value after a percentage was applied.
Reverse percentage
Undo a discount or an increase to find where the number started.
You paid a reduced price and want the original.
A value went up and you want the starting figure.
Recent calculations
Why reversing a percentage is not the same as applying one
The instinct is to apply the percentage again in the opposite direction, and that instinct is wrong every time. If a price rose 25% to reach 500, taking 25% off 500 gives 375 — but the true original was 400. The 25% was calculated on 400, not on 500, so the two percentages are slices of different-sized cakes.
The fix is division rather than subtraction. If a value has grown by 25%, it now represents 125% of the original, so dividing by 1.25 takes you back. The same logic applies to discounts: a price after 25% off is 75% of the original, so divide by 0.75.
How to use it
The first tab undoes a discount — useful when a receipt shows what you paid and the percentage saved but not the ticket price. The second tab undoes an increase, which is what you need for working back through a price rise, a salary increment or any figure that has grown by a known percentage.
The formulas
Worked examples
You paid 974.25 after 25% off
- After 25% off you pay 75% of the original
- Divide: 974.25 ÷ 0.75 = 1,299
- Check: 25% of 1,299 is 324.75, and 1,299 − 324.75 = 974.25 ✓
A figure of 1,416 after an 18% rise
- After an 18% rise the value is 118% of the original
- Divide: 1,416 ÷ 1.18 = 1,200
- Check: 18% of 1,200 is 216, and 1,200 + 216 = 1,416 ✓
Where this comes up
More often than you would expect. Recovering a list price from a discounted invoice. Finding a pre-tax figure when only the gross is shown — although the tax calculator is more direct for that. Working out last year's rent from this year's figure and the percentage rise. Reconstructing a starting salary from a current one after a known increment.
Common mistakes
Subtracting instead of dividing. The single biggest error, and the reason this calculator exists as a separate page.
Reversing a discount of 100% or more. If everything was taken off, there is no information left to work back from. The calculator explains this rather than dividing by zero.
Using the wrong direction. Undoing a discount means dividing by a number smaller than 1, which makes the answer larger. Undoing an increase divides by a number larger than 1 and makes it smaller. If your answer moved the wrong way, you are on the wrong tab.