Percentage Off Sale Price Calculator

Discount Calculation Guide

Sale Price Formulas

Sale price = Original × (1 − discount%/100). Saving = Original × discount%/100. To find original from sale price: Original = Sale price ÷ (1 − discount%/100). Example: £80 with 25% off = £80 × 0.75 = £60. Saving = £20. Working backwards: a £60 item after 25% off had an original price of £60 ÷ 0.75 = £80.

Spotting Misleading Discounts

'Was £100, now £80' — this is 20% off, not 25%. A common trick: items are marked up temporarily, then 'discounted' to appear as a better deal than the usual price. Check the price history using browser extensions like CamelCamelCamel for Amazon, or Pricespy for other retailers. UK trading standards require that the 'was' price must have been the genuine selling price for at least 28 days in the 6 months before the sale.

VAT and Discounts

When calculating discounts in a business context, be clear whether prices are inclusive or exclusive of VAT. A trade discount applied before VAT is more valuable than the same nominal discount applied after VAT. 20% discount on £100 ex-VAT = £80 ex-VAT (£96 inc). 20% off the £120 inc-VAT price = £96 — same number but the pre-VAT value differs. Trade prices and trade discounts are almost always quoted ex-VAT.

Compound Discounts

Multiple discounts do not add linearly. A 20% discount followed by a further 10% discount is NOT 30% off. It is 1 − (0.80 × 0.90) = 1 − 0.72 = 28% off. Example: £100 after 20% = £80. Then 10% off £80 = £72. Total saving: £28, not £30. This is why 'extra 10% off sale items' is always less valuable than it appears — the second discount applies to the already-reduced price.