The short answer
- Sale price = price × (1 − discount ÷ 100).
- Two discounts in a row multiply; they do not add.
- To find the original price, divide the sale price by what was left.
- Compare packs by unit price, not by the shelf price.
Working out a percentage off
- 25% of 8020
- 80 − 2060
A quicker way is to multiply by what is left. 25% off leaves 75%, so 80 × 0.75 = 60. The percentage calculator handles other percentage sums.
Money off as a percentage
A voucher for 10 off a price of 40 is worth 25%. The same voucher on a price of 200 is worth only 5%. To compare a money-off voucher with a percentage offer, divide the money off by the price and multiply by 100. Choose “money off” in the calculator to see the percentage.
Stacked discounts
“20% off, plus an extra 10% at the till” sounds like 30% off. It is not. The extra 10% is taken from the price that is already reduced.
- 20% off 10080
- 10% off 8072
Multiply what is left after each discount: 0.8 × 0.9 = 0.72, so you pay 72% of the price.
Stacked discounts at a glance
| First discount | Then | Total off | Not |
|---|---|---|---|
| 10% | 10% | 19% | 20% |
| 20% | 10% | 28% | 30% |
| 20% | 20% | 36% | 40% |
| 30% | 20% | 44% | 50% |
| 50% | 20% | 60% | 70% |
| 70% | 10% | 73% | 80% |
| 50% | 50% | 75% | 100% |
The bigger the discounts, the bigger the gap between the real total and the two percentages added together.
Does the order matter?
With two percentages, no: 0.8 × 0.9 is the same as 0.9 × 0.8. With a money-off voucher and a percentage, yes. On a price of 60:
- After 10 off
- 50
- After 20% off
- 40
- After 20% off
- 48
- After 10 off
- 38
Taking the percentage first and the fixed amount second gives the lower price, because the percentage applies to a bigger number.
Finding the original price
- 100% − 40%60%
- 45 ÷ 0.675
Do not add the percentage back
Adding 40% to 45 gives 63, not 75. The 40% was a share of the original price, which is larger than the sale price.
3 for 2 and buy one get one free
A multi-buy offer is a discount spread across several items. With items at 1.50 each:
| Deal | You get | You pay | Each | Same as |
|---|---|---|---|---|
| Buy 1 get 1 free | 2 | 1.50 | 0.75 | 50% off |
| 3 for 2 | 3 | 3.00 | 1.00 | 33.33% off |
| Buy 4 get 2 free | 6 | 6.00 | 1.00 | 33.33% off |
| Buy 3 get 1 free | 4 | 4.50 | 1.125 | 25% off |
The saving is real only if you use everything you buy. Food that goes off before you eat it makes the deal more expensive.
Unit prices
A unit price is the price for a set amount, such as per kilogram or per litre. In the UK, the Price Marking Order 2004 requires many shops to show unit prices for goods sold by weight or volume. Updated government guidance applies from 6 April 2026, including unit prices on promotions.
- 2.40 ÷ 0.5 kg4.80 per kg
- 3.30 ÷ 0.75 kg4.40 per kg
Bigger packs are often cheaper per unit, but not always, especially when the smaller pack is on offer.
VAT and sales tax
In the UK and the rest of Europe, prices shown to shoppers include VAT, so the discount comes off the price on the ticket. The UK standard rate of VAT is 20%: a price of 72 including VAT is 60 before VAT. Use the VAT calculator to split a price.
In most US states, sales tax is added at the till, after any discount. A 72 price with 7.25% sales tax comes to 77.22. Set the rate under More options, or use the sales tax calculator to find your state’s rate.
Was prices and reference prices
A “was” price should be a price the shop really charged. UK trading standards guidance says comparisons with earlier prices must not mislead shoppers. If a discount looks too good, check the price history or compare with other shops.
Quick mental shortcuts
- 10% off: move the decimal point one place left and take it off. 10% of 45 is 4.50.
- 20% off: find 10% and double it.
- 25% off: divide by 4 and take that off, or multiply by 0.75.
- 50% off: halve it.
- 15% off: find 10%, add half of it again.
Rounding at the till
Tills round to the penny or cent. Some round each item, others the total, and some round after each discount. That is why a receipt can differ from a calculation by a penny or two. This calculator only rounds the figures it shows you.
Is the deal worth it?
- Would you have bought it at full price? If not, the saving is not a saving.
- Compare the unit price with the shop’s own brand and other pack sizes.
- Check delivery charges and minimum spends online, which can cancel a discount.
- For a tip on a discounted bill, see the tip calculator.