Reverse percentage calculator
Find the original value before a percentage increase or decrease from the final value.
How do I use this page?
- Enter values or use the example in the form.
- Choose a mode or units where available.
- Read the result and check the calculation steps below.
What this page does not do: Enter a non-negative percentage. A decrease must be below 100% to recover a unique original value.
Further reading
Theory — how do you find a value before a percentage change?
The reverse percentage calculator finds the original value before a percentage increase or decrease, starting from the known final value. After a 20% increase an amount becomes 120, so the original value is found by dividing 120 by 1.2, giving 100. Likewise, after a 20% decrease an amount of 80 is divided by 0.8, again giving 100. A common mistake is subtracting 20% from the final value — that calculation does not recover the correct original amount.
Frequently asked questions
How is the result calculated?
What are the limitations?
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