Reverse Percentage Calculator
Find the original value before a percentage increase or decrease was applied. Enter the final value and the percentage change to work backwards to the starting number. Essential for tax-inclusive prices and markups.
How to use this tool
- Enter final value (after change) and percentage change applied in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your original value (before change) and the full breakdown beneath it.
Formula
Original = Final / (1 + Percentage/100)
How it works
Divide the final value by (1 + the percentage change expressed as a decimal) to recover the original pre-change value.
Worked example
Price is 120 after a 20% increase
- Divisor: 1 + 20/100 = 1.20
- Original: 120 / 1.20 = 100
Common mistakes to avoid
- Dividing the final value by the percentage instead of by (1 + Percentage/100), which gives the wrong original.
- Forgetting to adjust the sign for a decrease; for a 20% decrease the divisor is (1 - 0.20) = 0.80, not 1.20.
- Using this calculator when the percentage was applied to a different base, such as a tax stacked on another surcharge.
Key terms
Frequently asked questions
- A price tag shows $119 including 19% VAT. What was the pre-VAT price?
- Enter Final = 119 and Percentage = 19. The calculator computes 119 / 1.19 = $100 pre-VAT.
- How does this differ from subtracting the percentage from the final value?
- Subtracting 19% of 119 gives 96.39, which is wrong. You must divide by (1 + rate) because the percentage was applied to the unknown original, not the final price.
- Does this work for percentage decreases too?
- Yes. For a decrease, enter the final value and the percentage removed. The tool divides by (1 - rate) to reverse the decrease.