Reverse Percentage Calculator
Work backward from a percentage result to find the original value before an increase or decrease with this free reverse percent calculator.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the final value and the increase applied.
- Press Calculate.
How it works
Finds the original value before a percentage rise: original = final ÷ (1 + percent ÷ 100).
Worked example
$230 after a 15% rise. = $200 original.
Common mistakes
- Subtracting the percentage from the final figure — you must divide it out instead.
- Treating a price after a discount as the base for the discount.
Frequently asked questions
How do I find the original amount before a percentage?
Divide the final amount by (1 + rate) for an increase, or (1 − rate) for a decrease. 120 after a 20% rise was 120 ÷ 1.2 = 100.
How do I find a price before tax?
Divide the tax-inclusive price by (1 + tax rate). At 10% GST, divide by 1.1 to get the pre-tax amount.
When would I use a reverse percentage?
To strip a known markup or tax off a final figure — for example, finding the pre-GST price from a GST-inclusive total.
Related tools
- Percentage Increase Calculator
- GST Add Remove Calculator
- Percentage Decrease Calculator
- Percentage Difference Calculator
- Fraction to Percent Calculator
- Percent Error Calculator
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Cite this tool
Zerdly. (2026). Reverse Percentage Calculator. Retrieved from https://www.zerdly.com/tools/reverse-percentage-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.