How this calculator works
This calculator works backwards: you know a percentage and what it equals, and you want the original whole number. For example, “30 is 20% of what?” It helps when you know a deposit, a commission or a portion and need the full amount.
Divide the known amount by the percentage written as a decimal. If 30 is 20% of a number, the number is 30 ÷ 0.20.
Worked example: a $45 deposit that is 15% of the price
- Turn the percentage into a decimal: 15 ÷ 100 = 0.15.
- Divide the known amount by it: 45 ÷ 0.15 = 300.
- Check: 15% of 300 = 45. ✓
The full price is $300.
Quick reference: when 50 is a given percentage
| 50 is… | Divide by | Original number |
|---|---|---|
| 10% | 0.10 | 500 |
| 20% | 0.20 | 250 |
| 25% | 0.25 | 200 |
| 40% | 0.40 | 125 |
| 50% | 0.50 | 100 |
| 80% | 0.80 | 62.5 |
Common mistake
Adding the percentage back on. If an item costs $80 after 20% off, the original is not $80 + 20% = $96. It is $80 ÷ 0.80 = $100, because the 20% was taken from the original price, not the sale price.
Questions people ask
- How do I find a price before a discount?
- Divide the sale price by the share you paid. After 25% off you pay 75%, so a $60 sale price means $60 ÷ 0.75 = $80 originally. The discount calculator does this for you.
- How do I remove tax from a total?
- Divide the total by 1 plus the tax rate as a decimal. A $108 total with 8% tax was $108 ÷ 1.08 = $100 before tax.
- How do I check my answer?
- Take the percentage of your result. If it gives back the amount you started with, the answer is right.
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