02 · Original value
Calculation result
Before a 25% increase, the value was 100.
- Resulting value
- Reverse factor
- Change amount
Check
Work backwards with confidence
Find the value before the percentage changed.
Enter the resulting value and the percentage increase or decrease. The original value appears instantly, with the arithmetic shown.
Calculations stay in your browser. No data is sent or saved.
The method
Reverse the multiplier. Don’t subtract the percentage.
A percentage change is calculated from the original value. To go backwards, divide the result by the change factor.
Increase
After a p% increase
original = result ÷ (1 + p ÷ 100)
Example: 125 after a 25% increase gives 125 ÷ 1.25 = 100.
Decrease
After a p% decrease
original = result ÷ (1 − p ÷ 100)
Example: 75 after a 25% decrease gives 75 ÷ 0.75 = 100.
A common mistake
Why 25% off and 25% back are not opposites
If 100 increases by 25%, it becomes 125. But subtracting 25% from 125 gives 93.75—not 100—because the second percentage uses 125 as its base.
Reverse calculation restores the original base by dividing by 1.25. The check line in the result panel runs the percentage forward again so you can verify the answer.
Good to know
Quick answers
Can a decrease be 100%?
No unique original value can be recovered after a 100% decrease because every starting value becomes zero. For that reason, decrease percentages must be below 100%.
How are decimals handled?
Calculations use the full browser number value. Displayed answers use up to 12 decimal places, without changing the underlying result.
Can I share a calculation?
Yes. Use “Copy link” to copy a URL containing the resulting value, percentage, and direction. The parameters contain only the numbers shown in the form.