How to work out a discount
Sale price = original price × (1 − discount)
You save = original price × discount
For 25% off a $120.00 jacket: $120.00 × 0.75 = $90.00, a saving of $30.00. To find the original price from a sale price, divide instead: $90.00 ÷ 0.75 = $120.00.
Stacked discounts don't add up
"20% off, plus an extra 10% off" is applied one after the other, so the second discount comes off an already-reduced price. The total is 28% off, not 30%:
1 − (1 − 0.20) × (1 − 0.10) = 0.28
On a $120.00 item that's $86.40 instead of $84.00. The calculator does this for you when you enter an extra discount.
Things to know
- Check the "was" price. Under the FTC's pricing guides, a former price should be one the item was genuinely offered at. A big percentage off an inflated price isn't a real saving.
- Compare per unit. For groceries and household goods, the unit price calculator tells you which deal is really cheaper.
- Count it in work hours. A sale is only a saving if you'd have bought it anyway. See what it costs in your time with the cost in work hours calculator.
Questions people ask
How do I calculate 30% off?
Multiply the price by 0.70. On $80 that's $56, so you save $24. For any discount, multiply by 1 minus the percentage as a decimal.
Is tax charged on the original or the sale price?
Usually on the price you actually pay after a store discount. Manufacturer coupons can be treated differently in some states.
Sources
- FTC: Guides Against Deceptive Pricing (16 CFR Part 233)
- Tax Foundation: state and local sales tax rates, midyear 2026
Reviewed September 26, 2026 by The Dollars World team. How we build and check our calculators · Our data and formulas. This is general information, not financial advice.