Reverse Percentage Calculator
Original = Result ÷ (1 ± Percentage ÷ 100)120 ÷ (1 + 20 ÷ 100) = 100
Free online tool
Reverse Percentage Calculator
Know the result after a percentage change? Find the original number.
Instant calculation
Find the original value
Enter the result and what percentage change was applied.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter the result
Type the value after the percentage change.
- 02
Set the percentage
Type the percentage that was applied.
- 03
Choose direction
Enter 0 for increase or 1 for decrease.
- 04
Find original
The calculator reverses the percentage to find the starting value.
The formula
How this calculation works
For an increase: divide by (1 + percentage/100). For a decrease: divide by (1 − percentage/100). The calculator handles both cases.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
After 20% increase, result is 120. Original?
120 ÷ (1 + 20 ÷ 100) = 100100After 20% decrease, result is 80. Original?
80 ÷ (1 − 20 ÷ 100) = 100100Common questions
Questions about this calculation
What is a reverse percentage?
It finds the original value before a percentage change was applied. For example, if 120 is the result after a 20% increase, the original was 100.
How do I know whether to use increase or decrease?
If the final value is larger than the original, use increase (0). If smaller, use decrease (1). The calculator does the rest.
What happens with a 100% decrease?
A 100% decrease means the result should be 0. Asking for the original of 0 with a 100% decrease is mathematically undefined.
Where is reverse percentage useful?
Common uses include finding pre-sale prices, reversing tax or tip calculations, and working backwards from final to initial values.
Is this the same as the Percentage Calculator?
No. The main Percentage Calculator finds what a percentage of a number is. The Reverse Percentage Calculator works backwards from the result.
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