Reverse Percentage Calculator
Find the original number before a percentage increase or decrease was applied.
About Reverse Percentage Calculator
If a value was increased by P%, the final equals original × (1 + P/100). To reverse this, divide the final by that factor. Similarly, for a decrease divide by (1 − P/100).
Formulas
Reverse Percentage (increase)
Original = Final / (1 + P/100)
- Final
- The value after the increase
- P
- The percentage that was applied
Reverse Percentage (decrease)
Original = Final / (1 − P/100)
- Final
- The value after the decrease
- P
- The percentage that was applied
Worked example
With the default values below, Reverse Percentage Calculator returns Original Value of 100.0000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Final Value (after change)
- 120
- Percentage Applied
- 20
- Change Directionone of Increase (was added), Decrease (was subtracted)
- Increase (was added)
Results
- Original Value
- 100.0000
- Multiplier Used
- 1.2000
Step by step
- 1Determine the multiplier= 1.2
- 2Divide final value by multiplier= 100.000000
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why can't I just subtract the percentage from the final value?
Because the percentage was applied to the original, not the final. For example, 20% of 100 is 20, giving 120. But 20% of 120 is 24, not 20. You must divide, not subtract.
What is a practical use case?
Finding the pre-tax price: if an item costs $120 including 20% VAT, the pre-tax price is 120 / 1.20 = $100.