Live calculation
Instant percentage calculations · Private in your browser · No account required
Original / whole value100
The original value before the 20% decrease was 100.
Show calculation steps
- Remaining multiplier = 1 − 0.2 = 0.8.
- Divide 80 by the multiplier = 100.
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Private by design
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How this calculator works
Original after decrease = final ÷ (1 − percentage ÷ 100)
Reverse percentages are useful when you know the final number but need to reconstruct the starting number. The correct operation is division by the percentage multiplier, not simply adding the percentage back.
Example: $80 after a 20% discount
$80 represents 80% of the original price. Dividing 80 by 0.80 gives an original price of $100.
Frequently asked questions
Why can't I just add 20% back after a 20% discount?
Because the 20% discount was based on the larger original value. Adding 20% to the smaller final value uses a different base.
Can I reverse a 100% decrease?
No. Once the final value is zero after a 100% decrease, the original cannot be uniquely recovered from that information alone.