Working out a sale price is everyday percentage math — but stacked discounts hide a twist that stores quietly rely on. Here's how to calculate a discount, and why two discounts never add up to their sum.
How to calculate a percent-off discount
Multiply the price by the discount percentage (as a decimal) to get the savings, then subtract from the price for what you pay. A 25%-off item at $80 saves 80 × 0.25 = $20, so you pay $60. A shortcut: paying after a 25% discount means paying 75% of the price, so $80 × 0.75 = $60 directly.
Quick savings table
| Price | 10% off | 25% off | 50% off |
|---|---|---|---|
| $20 | $18.00 | $15.00 | $10.00 |
| $50 | $45.00 | $37.50 | $25.00 |
| $100 | $90.00 | $75.00 | $50.00 |
Do stacked discounts add up?
No — and this is the key insight. An extra 10% off an already 20%-off price is not 30% off. Apply them in sequence: $100 → 20% off → $80 → 10% off → $72. You paid $72, which is a 28% total discount, not 30%. The second discount is taken on the smaller, already-reduced price, so it removes less than the headline number suggests.
Discounts and tax
A discount applies to the pre-tax price; sales tax or VAT is then added to the discounted amount. So calculate the discount first, then the tax — see how to calculate VAT. And if you're on the selling side, margin vs markup explains how discounts eat into profit.