Discount Calculator
Sale prices and percent-off savings.
Details
Final price
$90.00
You save $30 (25%)
This works out a sale price from a discount percentage, and the amount saved.
It also handles stacked discounts and works backwards to find the original price from a sale price.
How discounts are calculated
A discount is a percentage taken off a price. An $80 item at 25% off saves $20 and costs $60. That much is straightforward.
What is not straightforward is stacking. Two discounts applied one after another do not add up. 20% off then a further 10% off is not 30% off — it is 28%, because the second discount applies to the already-reduced price.
On that $80 item, the stacked version costs $57.60 and a genuine 30% off costs $56. Small here, and material on anything expensive. Retailers use the wording carefully, and "an extra 10% off sale prices" always means the smaller discount.
Stacking 20% and 10% gives an effective 28%, not 30%. The second percentage is applied to the smaller number.
What to enter
- Original price
- The price before any reduction. If you only have the sale price and the percentage, use the reverse calculation.
- Discount percentage
- The reduction being applied. Multiple discounts are applied one after another, not added.
- Sales tax
- Usually applied to the discounted price, so it comes after the reduction. That means a discount also saves you the tax on the amount saved.
What this assumes
Discounts are treated as applying in sequence, which is how retailers apply them.
Sales tax is applied after the discount, which is standard practice in US retail.
How to calculate a discount
Multiply by what is left, not by what comes off. It makes stacked discounts easy.
- 1 − discount
- The fraction you still pay. 25% off means paying 0.75
- stacked
- Multiply the remaining fractions together, never add the discounts
Convert the discount to a decimal. 25% becomes 0.25. Subtract from 1 to get 0.75, which is the fraction you pay.
Multiply the price by it. $80 × 0.75 = $60. Subtract from the original for the amount saved.
For stacked discounts, multiply the fractions. 20% then 10% is 0.8 × 0.9 = 0.72, so you pay 72% and the effective discount is 28%.
To reverse, divide. A $60 item at 25% off had an original price of $60 ÷ 0.75 = $80.
See a worked example: why 20% and 10% is not 30%
- Original price
- $80
- Offer
- 20% off, then an extra 10% off
First discount: $80 × 0.80 = $64.
Second discount: $64 × 0.90 = $57.60.
Combined: $80 × 0.72 = $57.60, an effective 28% discount.
A straight 30% off would be $56.00, so the stacked offer costs $1.60 more. On a $2,000 purchase the same gap would be $40.
$57.60, an effective 28% off
Frequently asked questions
No. Each discount applies to the price after the previous one, so they compound downwards rather than adding.
20% then 10% is an effective 28%, not 30%. Multiply the remaining fractions: 0.8 × 0.9 = 0.72, so you pay 72%.
Mathematically no, because multiplication is commutative: 0.8 × 0.9 is the same as 0.9 × 0.8.
In practice it can matter, because retailers set rules about what applies to what. A coupon that only works on full-price items behaves very differently from one that works on sale prices.
Divide by the fraction you paid. A $60 item after 25% off was $60 ÷ 0.75 = $80.
Do not add the percentage back. Adding 25% to $60 gives $75, which is wrong, because the 25% was calculated on the larger original figure.
Before, in normal US retail. Tax is charged on what you actually pay.
That makes a discount slightly better than it looks: at an 8.25% rate, saving $20 also saves $1.65 of sales tax.
Yes, if you buy exactly two identical items. Two at $80 with the second half price is $120 for $160 of goods, which is 25% off.
It is only that good if you actually wanted two. If you would have bought one, you have spent $120 instead of $80 to save a notional $40.
Convert one to the other. $20 off an $80 item is 25%. $20 off a $200 item is 10%.
Dollar-amount coupons are worth proportionally more on cheaper items, and percentage discounts are worth more on expensive ones. Where both are available, that is the rule of thumb.
Problems people actually run into
Adding stacked percentages together
"30% off plus an extra 20%" reads like 50% off. It is 44%, because 0.7 × 0.8 = 0.56, so you pay 56%.
On a $2,000 purchase that is $1,120 rather than the $1,000 you expected. Multiply the remaining fractions and you will never get this wrong.
Judging a deal by the discount rather than the price
A 60% discount from an inflated "original" price can leave you paying more than a 20% discount elsewhere. The percentage describes the retailer's own reference price, which they set.
Compare final prices between sellers. The size of the discount tells you about the marketing, not about the value.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: September 4, 2026