Discount Calculator
Sale price, savings amount, and effective discount from price and percent off
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What this calculator computes
The discount calculator computes the sale price and the cash savings when a percentage discount is applied to an original price. Inputs are the original price and the discount percentage; outputs are the savings amount (the dollars off), the final sale price, and the percentage paid (100% minus the discount). The math is straightforward — savings = price × (discount% / 100), sale price = price − savings — but the calculator's value is in handling chained discounts ("30% off plus an extra 20%"), tax-inclusive sale prices ("£99 inclusive of 20% VAT, after 25% off"), and the common "save X%" vs "% off" framings that retailers use somewhat interchangeably. A 25% discount on $80 saves $20 and leaves a $60 sale price; chaining "an extra 20% off the sale price" further reduces it to $48, giving a 40% effective discount on the original (not 45%, which is the naive sum). The calculator can be run twice to compute the effective compound discount for chained markdowns. It also reverses the calculation: given a sale price and the percentage discount, it back-computes the original price, useful for comparing "was £80, now £60" claims against actual fair market prices when the "was" price is suspect. UK and EU readers should note that VAT-inclusive sale prices behave the same way under percentage discounts — the discount applies to the gross price including VAT — but VAT itself is not discounted; HMRC treats the post-discount price as the new VAT-inclusive base.
Calculator
The formula
Formula
savings = price × (discount% / 100) sale_price = price − savings
Worked example
When to use this calculator
Use this calculator any time a price is shown with a percentage discount and you want to know the actual sale price or savings amount, or when chaining multiple discounts that don't simply add. The most common cases are retail shopping (verifying advertised "X% off" claims), Black Friday and Cyber Monday stacked discounts (where promotions chain on top of the marked sale price), seasonal clearance pricing, coupon and voucher application, and reverse-calculating an original price from a sale price (testing whether the "was" price is realistic). The calculator is also useful for budgeting and comparison shopping, where two competing offers (e.g., "30% off £120" vs "20% off £100") need to be compared on the actual cash basis rather than the headline percentage. It does not handle tiered discounts where different percentages apply to different price bands; for those, run multiple calculations and sum.
Common input mistakes
- Adding chained discount percentages directly. "30% off plus another 20% off" is not a 50% discount but a 44% effective discount, because the 20% applies to the already-reduced 70% balance: 0.70 × 0.80 = 0.56, so the customer pays 56% (44% off). Retailers exploit this confusion regularly; always compute compound discounts multiplicatively.
- Comparing percentage discounts across different base prices. "40% off £100" and "30% off £150" have similar headline percentages but very different cash outcomes (£40 saved vs £45 saved, leaving £60 vs £105 to pay). Always compare the cash-out price between competing offers, not the percentage.
Frequently asked questions
How do I calculate a discount?
Multiply the original price by the discount percentage expressed as a decimal: savings = price × (discount% / 100). Then subtract the savings from the original price to get the sale price. A 30% discount on £120 saves £120 × 0.30 = £36, leaving a sale price of £120 − £36 = £84. Equivalently, the customer pays 100% − 30% = 70% of the original, and £120 × 0.70 = £84.
How do stacked discounts work?
Stacked or chained discounts apply multiplicatively, not additively. "30% off plus an extra 20%" means the second 20% applies to the already-reduced price, giving an effective discount of 1 − (0.70 × 0.80) = 1 − 0.56 = 44%, not 50%. Compute by applying each discount in sequence: £120 × 0.70 = £84, then £84 × 0.80 = £67.20, giving £52.80 total savings on the £120 original.
How do I find the original price from a sale price?
Divide the sale price by (1 − discount/100) to recover the original price. A £84 sale price after 30% off was originally £84 / (1 − 0.30) = £84 / 0.70 = £120. This is useful for verifying retailers' "was" prices against current sale prices — if the back-computed "original" is suspiciously high or doesn't match historical pricing, the discount may be inflated.
Does the discount apply before or after VAT or sales tax?
Typically the discount applies to the gross (tax-inclusive) price in UK/EU, where prices are displayed VAT-inclusive, and to the net (pre-tax) price in the US, where sales tax is added at the till. In both cases the customer pays tax on the post-discount amount, not the original. A £120 VAT-inclusive jacket at 30% off costs £84 including VAT; HMRC sees the £84 as the new VAT-inclusive sale.
How do I compare two discounts on different items?
Compare the absolute cash savings rather than the percentage. "40% off £100" saves £40 and leaves £60 to pay; "30% off £150" saves £45 and leaves £105 to pay. The percentage is irrelevant in isolation; what matters is which deal leaves the lower out-of-pocket cost for equivalent items. The percentage is only useful when comparing different discount levels on the same item.