Reverse a Percentage, Increase or Discount
Find the whole behind a percentage amount or recover a value before an increase or discount. Adding the same percentage back to the final amount uses a different base and generally gives the wrong original.
- Runs in your browser
- Nothing is uploaded
- No signup; device limits apply
Numbers stay on your device. Nothing is sent to a server.
How to use this tool
Enter the known value and percentage, then choose percent-of-whole, before-increase or before-decrease mode. A 100% decrease loses the original information and cannot be uniquely reversed.
Results and examples
Divide by the fraction, one plus the fraction or one minus it as appropriate. Units remain unchanged, and rounding in the known final amount can affect the reconstructed original.
Worked example
After a 20% discount, 80 implies 80/0.8 = 100, not 96 from adding 20% to 80.
Limitations
- Stacked discounts and intermediate rounding differ from one percentage change.
- A 100% reduction has no unique inverse.
Fields
| Field | Guidance and constraints |
|---|---|
| What you know | This amount is P% of what original? / After a P% increase, the value is this — what was it before? / After a P% decrease, the value is this — what was it before? |
| Known amount | Accepted range: -1000000000–1000000000 · Input step: 0.01 |
| Percent | Accepted range: -1000–1000 · Input step: 0.01 |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
Why not add the discount back?
The final and original values use different percentage bases.
Does it convert currency?
No. The result keeps the units of the entered number.
Related tools
You do not need to start over. Continue with the tool that fits your next step.
