To reverse a percentage increase, divide the result by (1 + percentage ÷ 100). To reverse a decrease, divide by (1 − percentage ÷ 100). For example, if 230 is the result of a 15% increase, the original value was 230 ÷ 1.15 = 200.
This is the same engine as the main Percentage Calculator below, using its "Reverse %" tab — for when you know the final number and the percentage that was applied, and need to work backward to what it started as.
How it works
Enter the final value and the percentage that was applied, and specify whether it was an increase or a decrease. For an increase, original = final ÷ (1 + percent ÷ 100). For a decrease, original = final ÷ (1 − percent ÷ 100). This is the inverse of the everyday "increase/decrease by %" calculation.
Examples
- 230 after a 15% increase original was 200
- 45 after a 10% decrease original was 50
- 212.50 after a 15% decrease original was 250
Related questions
- When would I need to reverse a percentage?
- Common cases: a price already includes a discount or tax and you want the pre-discount/pre-tax amount, or you know a final measurement and the percentage change but not the starting figure.
- Why can't I just subtract the percentage back out?
- Because the percentage was applied to the ORIGINAL value, not the result — subtracting X% of the result doesn't undo adding X% of the original. Dividing by (1 ± percent ÷ 100) is the correct inverse operation.