How to calculate a discount
To find a sale price, work out how much of the price you still pay, then multiply. A 25% discount means you pay 75% of the original.
sale price = original × (1 − discount ÷ 100)
you save = original − sale price
Example: a jacket costs 80 and is 25% off.
1 − 0.25 = 0.75, and 80 × 0.75 = 60. You save 20.
Stacked discounts: why 20% + 10% isn't 30%
Shops often advertise "an extra 10% off sale prices." The second discount is taken from the already reduced price, so the total is always a bit less than the two numbers added together.
A 100 item with 20% off, then an extra 10% off:
100 × 0.80 = 80, then 80 × 0.90 = 72. The total discount is 28%, not 30%.
The order doesn't matter: 10% then 20% gives the same 72. Enter the second discount in the "extra discount" box above to see the true combined saving.
Quick discount math in your head
- 10% off: move the decimal one place left and subtract. 10% of 45 is 4.50, so you pay 40.50.
- 20% off: double the 10% figure. 20% of 45 is 9, so you pay 36.
- 25% off: divide by 4. A quarter of 80 is 20, so you pay 60.
- 50% off: halve it.
- 15% off: 10% plus half of 10%. For 60, that's 6 + 3 = 9 off.
Is it really a good deal?
A big percentage off isn't always a good price. Before you buy, check:
- The real starting price. Some sellers raise a "was" price just before a sale so the discount looks bigger. Price-history tools and comparing other shops help here.
- Shipping and fees. A 15% saving can disappear if delivery costs more than elsewhere.
- Price per unit. For groceries, compare the price per 100 g or per item, not the discount badge.
- Whether tax is added after. In many US states, sales tax is added at the till to the discounted price. Use the sales tax calculator to get the final amount.
Finding the original price from a sale price
If you know you paid 63 after a 30% discount, divide by the share you paid: 63 ÷ 0.70 = 90. Don't add 30% back on (63 × 1.30 = 81.90 is wrong), because the 30% was taken from the larger original price.
Frequently asked questions
How do I work out what percentage off something is?
Subtract the sale price from the original price, divide by the original, and multiply by 100. From 120 to 90: 30 ÷ 120 × 100 = 25% off. The percentage calculator does this with its change mode.
Does this calculator include tax?
No. It shows the price after discounts only. Where tax is added at checkout, put the sale price into the sales tax calculator.
Which is better: 30% off or "buy 2, get 1 free"?
Buy 2, get 1 free is 33.3% off per item, but only if you actually want three. If you only need one or two, the straight 30% off is better.
Last reviewed November 2026.