How to Calculate a Discount
Calculating a discount is one multiplication and one subtraction. This guide walks through each version of the calculation — the sale price, the amount saved, the discount percentage and the original price — with worked examples you can check, explains how discount and tax combine, and shows the mistakes that cost people money.
How to calculate a discount — step by step
Find the amount of the discount
Multiply the original price by the discount percentage. For example, 25% off an $80 item is $80 x 25% = $80 x 0.25 = $20. That $20 is the amount you save.
Subtract it to get the sale price
Take the discount amount off the original price. $80 - $20 = $60. So the sale price is $60.00. The shortcut is one step: $80 x (1 - 0.25) = $80 x 0.75 = $60.
Work out the discount percentage from two prices
If you know the original price and the sale price, the discount percentage is (original - sale) / original x 100. An item reduced from $80 to $60 is ($80 - $60) / $80 x 100 = 25% off.
Work backwards to the original price
If you know the sale price and the discount, divide: original = sale / (1 - discount % / 100). A $60 sale price at 25% off means the original price was $60 / 0.75 = $80.00.
Add tax after the discount, not before
Shops discount first, then charge tax on the discounted price. A $100 item at 10% off is $90, and 8% tax on $90 is $7.20, so the total is $97.20. Taxing the full $100 first would wrongly give $98.00.
Check the deal before you buy
Compare the sale price with the price elsewhere, and check whether the discount is on the real original price. A big percentage off an inflated price is not a bargain — the sale price itself is what matters.
Discount calculation examples
| What you want | Formula | Example |
|---|---|---|
| Sale price | original x (1 - discount % / 100) | $80 x (1 - 25%) = $80 x 0.75 = $60.00 |
| Amount saved | original x discount % / 100 | $80 x 25% = $20.00 saved |
| Discount percentage | (original - sale) / original x 100 | ($80 - $60) / $80 x 100 = 25% off |
| Original price | sale / (1 - discount % / 100) | $60 / (1 - 25%) = $60 / 0.75 = $80.00 |
| Discount + tax | discount first, then tax on the sale price | $100 - 10% = $90, + 8% tax = $97.20 |
| Double discount | apply one discount, then the next on the result | $100 - 20% = $80, then - 10% = $72.00 (not 30% off) |
All examples use exact maths to the cent. Use the free calculators on the home page for your own prices.
Five tips for calculating discounts
- Two discounts do not add up: A 20% discount followed by 10% off is not 30% off. The second discount applies to the already-discounted price: $100 - 20% = $80, then - 10% = $72.00, which is 28% off in total.
- A percentage off is not the same as a fixed amount off: $20 off an $80 item is 25% off, but $20 off a $200 item is only 10% off. Always compare percentages against the same original price.
- Round only at the end: Keep the full number while you calculate and round to cents only for the final answer. Rounding in the middle can put the result a cent or two out.
- Check the original price is real: Some shops raise the price before a sale so the discount looks bigger. If the item was never really sold at the original price, the percentage means nothing — judge the sale price itself.
- Tax is on the discounted price: In almost every shop, tax is charged after the discount. If a receipt charges tax on the full price before the discount, ask about it — that is not the usual order.
Frequently asked questions
What is 25% off $80?
25% of $80 is $20, so the sale price is $80 - $20 = $60.00 and you save $20.00. Use the first calculator on the home page for your own numbers.
How do I calculate 10% off a price?
Move the decimal point one place left: 10% of $100 is $10, so the sale price is $90. For any other percentage, multiply the price by the percentage and divide by 100.
How do I find the original price before a discount?
Divide the sale price by (1 - discount % / 100). For example, a $60 sale price at 25% off was originally $60 / 0.75 = $80.00.
How is discount and tax calculated together?
Discount first, then tax on the discounted price. $100 at 10% off is $90; 8% tax on $90 is $7.20; the total is $97.20. The fifth calculator on the home page does this in one step.
Does this site store my prices?
No. Every calculation happens in your browser and your numbers are never sent to any server or stored anywhere.