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Reverse percentage calculator
Enter a value and the percentage it represents and get the whole, for example if 30 is 25% of a number, the number is 120. Useful to undo a discount or a tax.
- Free
- No sign-up
- Runs in your browser
What is X% of Y?
X is what percent of Y?
Percentage change from A to B
Increase or decrease an amount by a percentage
X is P% of what number?
100% private — the calculation is done in your browser and nothing is sent to any server.
Next step
Keep going with your result in another tool. Nothing is uploaded.
How it works
Read the answer
The result appears at the top of the list.
Check the formula
The formula is shown under each result.
How to calculate a reverse percentage
To calculate a reverse percentage, divide the known value by the percentage as a decimal. If 30 is 25% of a number, the number is 30 ÷ 0.25 = 120. In the calculator above, enter the value and the percentage in the section X is P% of what number, and the whole appears at the top of the results.
The formula
Whole = value ÷ (percentage ÷ 100). The percentage is the share that the value represents of the unknown whole, so it cannot be zero.
A worked example, step by step
A jacket is on sale for 60 after a 25% discount, and you want the original price. Step 1: the sale price is 100% − 25% = 75% of the original. Step 2: turn 75% into a decimal, 0.75. Step 3: divide, 60 ÷ 0.75 = 80. The original price was 80. Check it forwards: 25% of 80 is 20, and 80 − 20 = 60. The same idea works for taxes, tips, commissions and growth.
Examples
| Known value | Is this percent | Whole number |
|---|---|---|
| 30 | 25% | 120 |
| 45 | 15% | 300 |
| 12 | 8% | 150 |
| 60 | 40% | 150 |
| 9 | 120% | 7.5 |
Undoing a discount or a tax
- Original price after a discount: if a sale price of 60 is 75% of the original, the original was 80.
- Price before tax: a total of 121 that is 121% of the net price means the net price was 100.
- Total from a share: if 45 people are 15% of a group, the group has 300.
A common trap
To undo an increase of 20%, do not decrease by 20%. A price of 120 after a 20% rise was 100 before, and 20% off 120 is 96. The correct method is to treat 120 as 120% of the original and divide by 1.2.
Private by design
The calculation runs in your browser as you type. The amounts you enter are never sent to a server, so you can use real prices, invoices and quotes.
Frequently asked questions
What is a reverse percentage?
A calculation where you know the result of applying a percentage and want the original value.
How do I find the original price before a 20% discount?
Divide the sale price by 0.8. For example, £80 ÷ 0.8 = £100.
How do I find the original price before a 20% increase?
Divide by 1.2. For example, 120 ÷ 1.2 = 100.
Is this converter free?
Yes. There is no sign-up and no limit, and it runs in your browser, so nothing you type is sent to a server.
Does it work on a phone?
Yes. It works in any modern mobile browser, and the result updates as you type.
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