Before a 20% discount
A price is 80 after a 20% reduction. What was it before?
After a 20% reduction, 80% of the original remains. Divide 80 by 0.8 to get 100. Adding 20% to 80 gives 96 because that uses a different base.
100
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Reverse percentage calculator
Work backward from a final price, salary, population, score, or other value after a known percentage change.
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Original value100
80 ÷ (1 − 20%)
Find the original value: worked examples
Choose whether the final value follows an increase or a decrease. Load a worked example to see how the original value is recovered.
Before a 25% increase
A value is 150 after increasing by 25%. What was the starting value?
The final value is 125% of the starting value. Divide 150 by 1.25 to get 120; the increase was 30.
120
Before a 5% reduction
A value is 190 after decreasing by 5%. What was it before?
95% of the original remains, so 190 ÷ 0.95 = 200. The reduction was 10, which is 5% of 200.
200
A 100% decrease cannot be reversed
A 100% decrease leaves zero for every original value. Dividing by the remaining fraction would divide by zero, so the original cannot be recovered from that percentage alone.
Use the forward calculation when the original is known
If you already know the original price and discount, calculate the final price directly.
Calculate a discounted priceFrom question to answer in three moves.
01
Enter the final value you already know.
02
Enter the percentage and choose increase or decrease.
03
See the value before the change.
FORMULA & LIMITS
The calculation is visible, not a black box.
This reverses one percentage change, not a series of changes. A 100% decrease cannot be reversed uniquely; an increase of −100% also produces a zero divisor. Check the selected direction and the meaning of negative values.
Formula usedbefore increase = final ÷ (1 + rate ÷ 100)before decrease = final ÷ (1 − rate ÷ 100)
Calculation checks updated 27 September 2026: automated tests cover sample inputs and numeric boundaries, not every possible input or commercial rule.
CLEAR ANSWERS
Math without mystery.
How do you reverse a percentage decrease?+
Divide the final value by 1 minus the percentage as a decimal. After a 20% decrease, divide the result by 0.8.
How do you reverse a percentage increase?+
Divide the final value by 1 plus the percentage as a decimal. After a 20% increase, divide the result by 1.2.
Why is reversing 20% not the same as adding 20%?+
The forward and reverse calculations use different base values, so equal percentage moves do not cancel each other by simple addition.