About the Reverse Percentage Calculator
Find the original value before a percentage increase or decrease — e.g. the price before tax or before a discount.
Also known as: original number before percentage, reverse percent, find original value, undo percentage.
How to use this calculator
- Enter final value, percentage change applied.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Open “Step-by-step” to see how the answer was worked out.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
Original = Final ÷ (1 + p/100)
Worked example
Using the values pre-filled in the calculator above:
- Final value = 115
- Percentage change applied = 15 %
the calculator returns:
- Original value: 100
- Amount of change: 15
Working
115 ÷ (1 + 15/100) = 100
Tips & common mistakes
- Do not subtract the percentage from the final value — 115 − 15% ≠ 100. Divide by 1.15 instead.