Reverse Percentage Calculator
Know the percentage that was applied and the result, but not the original number? This calculator works backwards to find it. Common uses: finding the pre-discount price of a sale item, the pre-tax price from a receipt total, or the original value before a percentage increase was applied. The most common mistake: entering the discount percentage instead of the remaining percentage — if something is 20% off, you enter 80 (what remains), not 20.
When to use this calculator
Use this when you have a final value and the percentage that produced it, and need to recover the starting figure — for example, a sale item at $68 after 15% off, a post-tax receipt of £94 at 17.5% VAT, or a final score that represents 80% of total marks.
Original Value
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Results are instant — nothing is stored and no account is needed.
Related Calculators
How to Calculate
- Enter the percentage in the first field — the percentage that was applied to the original.
- Enter the known result — the value that represents that percentage of the original.
- The original value is calculated instantly.
Formula
Divide the known result by the percentage, then multiply by 100. For example: 30 is 15% of what? (30 / 15) × 100 = 200.
Examples
30 is 15% of what?
200
45 is 90% of what?
50
63 is 70% of what?
90
Use Cases
- Finding the original price before a percentage discount
- Calculating pre-tax prices from post-tax receipt totals
- Working out the original salary before a pay cut
- Reversing a percentage change to find the starting value
- Determining total marks from a percentage score
FAQ
20 is 25% of what number?
20 is 25% of 80. Calculation: (20 / 25) × 100 = 80.
15 is 30% of what number?
15 is 30% of 50. Calculation: (15 / 30) × 100 = 50.
What is a reverse percentage?
A reverse percentage works backwards from a known result and a known percentage to find the original value. For example: if 40 is 20% of something, the original is 200.
How do I find the original price before a discount?
If an item costs £80 after a 20% discount, 80% of the original remains. Enter 80 as the percentage and 80 as the result — the calculator returns £100. Do not enter the discount (20%); enter the remaining percentage (80%). For the full discount and final price in one step, use the discount calculator instead.
50 is 10% of what number?
50 is 10% of 500. Calculation: (50 / 10) × 100 = 500.
How do I find a pre-tax price from a total that includes tax?
If a total of £108 includes 8% tax, then 108% of the original price = £108. Enter 108 as the percentage and 108 as the result — the original pre-tax price is £100. You can also use the sales tax calculator to verify the tax amount and total.