Reverse Percentage Calculator
Know the final amount and the percentage, but not where you started? Choose increase or decrease, enter the numbers, and the calculator finds the original value.
Results update as you type.
- Original value
- 120
- Amount of the change
- 18
Steps
- Multiplier = 1 + 0.15 = 1.15
- 138 ÷ 1.15 = 120
Worked example
Example: $138 including 15% markup — what was the cost?
- Multiplier = 1 + 0.15 = 1.15
- 138 ÷ 1.15 = 120
The original value was $120 (not $138 − 15% = $117.30).
Formula
Original = Final ÷ (1 + p/100) for an increase
Original = Final ÷ (1 − p/100) for a decrease
The common mistake is subtracting the percent from the final value, which uses the wrong base.
Frequently asked questions
How do I remove sales tax from a total?
Divide by 1 + the tax rate. A $53.50 receipt with 7% tax: 53.50 ÷ 1.07 = $50.00 before tax.
What was the price before a 30% discount if I paid $56?
56 ÷ (1 − 0.30) = 56 ÷ 0.70 = $80.
Why can't I just subtract the percentage?
Because the percentage was applied to the original number, not the final one. The base is different.
Last reviewed October 17, 2026 · Calculations run in your browser; nothing you enter is sent to a server.