Percentage guide
Reverse Percentage Calculator
A reverse percentage calculation finds the original value when you know the final amount after a percentage change. It helps when a sale price, tax-inclusive total, or increased figure is known but the starting amount is not.
Work backwards from a percentage change
Enter the final value, the percentage change, and whether it was an increase or decrease.
The interactive calculator loads with the page so you can enter your own values and see the result instantly.
How to calculate reverse percentage
Do not subtract the percentage directly from the final amount. First convert the percentage to the multiplier that created the final value, then divide by that multiplier.
Formula: original value = final value ÷ (1 ± percentage ÷ 100)
- Turn the percentage into a decimal and add it to 1 for an increase, or subtract it from 1 for a decrease.
- Divide the final value by this multiplier.
- The result is the value before the percentage change.
Example: $90 after a 10% discount
A 10% discount means the final price is 90% of the original, or 0.90. Divide $90 by 0.90 to get $100, the original price.
Frequently asked questions
How do you reverse a percentage increase?
Divide the final value by 1 plus the increase as a decimal. If 120 includes a 20% increase, calculate 120 ÷ 1.20 = 100.
How do you reverse a percentage discount?
Divide the sale price by the percentage left after the discount. For a 10% discount, divide by 0.90 because 90% of the original price remains.
What was the original price if $90 is 10% off?
A 10% discount leaves 90% of the original price. Divide $90 by 0.90 to get an original price of $100.
Why can’t I just subtract the percentage?
The final value is already the changed amount. Reversing the change requires division by its multiplier, not subtracting a percentage of the final value.
Can I reverse a 100% decrease?
No. A 100% decrease produces zero from every positive original value, so the original value cannot be determined.
Does reversing a 20% increase mean subtracting 20%?
No. Reverse a 20% increase by dividing by 1.20. Subtracting 20% from the final value uses the wrong baseline.
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