Discount Calculator

This calculator works out the final price after a percentage discount, the amount you save and, for stacked discounts, the combined effective percentage off. Enter the original price and one or more discount percentages to see results instantly. The formula behind it multiplies the original by one minus the discount over 100, so an £80 jumper at 25% off comes down to £60 and the saving is £20.

Stacked discounts are applied sequentially, not added together. A 20% discount followed by a 10% discount is not 30% off. It is 28% off, because the second discount applies to the already-reduced price, and 0.80 multiplied by 0.90 leaves 0.72 of the original. The same arithmetic turns 50% plus 25% into 62.5% off rather than 75%. Order makes no mathematical difference, though retailers sometimes apply codes only to certain items, or only after sale prices have come off, so the basket total is the figure to check.

You can also reverse-calculate by entering the sale price and the original price to find the percentage discount that was applied. Turn the formula round and the original equals the sale price divided by one minus the discount over 100, so £60 marked as 25% off must have started at £80. That is useful for checking whether a sale is genuine or whether the original price was inflated to make the reduction look larger than it is.

A few shortcuts make the arithmetic quick without a calculator. Taking 10% off means dividing by 10, while 25% off is a division by 4 and 33% off comes close to dividing by 3. Half price needs no explanation, 75% off leaves a quarter of the ticket, and 90% off leaves a tenth, which is the price multiplied by 0.1. The saving itself is the original multiplied by the discount over 100, which is often the easier figure to check against a receipt.

UK pricing law sets limits on how a reduction may be advertised. The unfair commercial practices rules in the Digital Markets, Competition and Consumers Act 2024, which replaced the Consumer Protection from Unfair Trading Regulations 2008 on 6 April 2025, require honest reference pricing, so a was price has to reflect a genuine higher price at which the item actually sold for a meaningful period beforehand; trading standards guidance has long used 28 consecutive days as a rule of thumb. Trading Standards investigate complaints, misleading pricing can void the sale, and the ASA rules on advertising claims. Price history tools including CamelCamelCamel for Amazon UK, PriceSpy and Idealo show 90-day tracking across major retailers, which settles most arguments about whether a headline is real.

VAT changes the order of operations depending on who is buying. On the VAT-inclusive prices used in consumer shops the discount comes off the gross figure and the VAT is already embedded, so £120 at 20% off becomes £96 and the VAT inside it falls from £20 to £16. On VAT-exclusive B2B invoices the discount comes off the net first and VAT is added afterwards, so £100 net less 20% is £80, and adding 20% VAT gives £96 gross. Trade and bulk-purchase discounts reduce the VAT base. Settlement discounts for prompt payment need the VAT to reflect what was actually paid, so the invoice is adjusted if the customer takes the discount.

Headline claims deserve suspicion. Up to 80% off usually applies to a handful of clearance lines rather than the range, which is how much Black Friday advertising works. More dependable savings come from retailer email sign-ups, where first-order codes run 10-15%, from timing purchases for the May and August bank holiday weekends, late November, or Boxing Day into January for white goods and clothing, and from stacking cashback sites such as TopCashback or Quidco for another 3-8%. Tesco Clubcard prices give members 50% off selected items, and student schemes through UNiDAYS or Student Beans add 10-15%, often valid up to 25.