How to Use the Percentage Reverse Calculator
When you only know a value after it changed and the percentage rate of that change, this tool works backward to find the original value. For example: "I bought something for $80 after a 20% discount — what was the original price?" or "My salary rose 15% to $46,000 — what was it last year?"
The math is simple but easy to get wrong. For an increase, original value = changed value ÷ (1 + rate/100). For a decrease, original value = changed value ÷ (1 − rate/100). Simply adding or subtracting the percentage from the changed value gives the wrong answer, since the rate was applied to the original value, not the changed one.
Frequently Asked Questions
It works backward from a changed value and its percentage rate to find the original value — for example, "If a price rose 20% to $120, what was the original price?"
Yes. For an increase: original = changed value ÷ (1 + rate/100). For a decrease: original = changed value ÷ (1 − rate/100).
A 100% decrease means the original value became zero, making reversal impossible. Enter a rate below 100%.