Reverse Percentage Calculator
Work backward from a final amount. Enter a positive percentage for an increase or a negative percentage for a decrease, and the calculator reverses the multiplier instead of simply subtracting the same percentage.
Pure percentage arithmetic. It assumes one multiplicative percentage change and does not model stacked discounts, tax-order rules, fees, rounding sequences, or a 100% decrease, which cannot be reversed from the final value alone.
Enter your scenario
Use the details that match your situation. Your estimate stays in this browser.
How this estimate works
- Convert the signed percentage change to a multiplier by calculating 1 plus percentage divided by 100.
- Divide the final value by that multiplier to recover the original value.
- A decrease must be entered as a negative percentage; reversing a 20% decrease divides by 0.80 rather than adding 20% to the final value.
Official percentage references
- NIST Special Publication 330: percent means parts per hundred
- NIST SI unit rules: percent and percentage-difference notation
NIST defines percent as parts per hundred. The reverse calculation follows directly from undoing a multiplicative percentage change.
Frequently asked questions
How do I reverse a 20% increase?
Divide the final value by 1.20. Subtracting 20% from the final value would not exactly undo the original increase.
How do I enter a percentage decrease?
Enter it as a negative value. For example, enter -20 for a final value that is 20% below the original.