Discount Calculator
Sale price and how much you save
Enter a price and a discount to get the sale price and what you save. This discount calculator also handles the case that trips everyone up: a second, stacked discount. An extra 10% off an already 20%-off price is 28% off, not 30% — and it adds sales tax on top if you want the real till figure.
Working out a sale price
The arithmetic is price × (1 − discount ÷ 100). An $80 jacket at 30% off is $80 × 0.70 = $56.00, saving $24.00. As a percent off calculator or a sale price calculator the maths is trivial; the value is in getting the awkward cases right, and there are three of them.
Stacked discounts multiply, they do not add
"20% off, plus an extra 10% off at checkout" is not 30% off. The second discount applies to the already-reduced price, so $100 becomes $80, then $72 — an effective 28%.
| First discount | Second discount | Looks like | You actually pay | Real discount |
|---|---|---|---|---|
| 10% | 10% | 20% | $81.00 | 19% |
| 20% | 10% | 30% | $72.00 | 28% |
| 25% | 20% | 45% | $60.00 | 40% |
| 30% | 20% | 50% | $56.00 | 44% |
| 40% | 20% | 60% | $48.00 | 52% |
| 50% | 20% | 70% | $40.00 | 60% |
| 50% | 30% | 80% | $35.00 | 65% |
| 50% | 50% | 100% | $25.00 | 75% |
On a $100 item. The gap between the advertised sum and the real discount widens as the discounts grow.
The last row is the clearest illustration: 50% off twice is 75% off, not free. The gap between what stacked offers sound like and what they deliver is a few points on small discounts and fifteen points or more on large ones, which is precisely why retailers advertise them that way.
Discount first, tax second
Sales tax is charged on what you actually pay, not the ticket price, so the discount comes off first. An $80 item at 30% off with 7.25% tax is $56.00 plus $4.06 of tax — $60.06 at the till.
Getting the order backwards inflates the tax, and the error compounds if you also stack discounts. Enter the tax rate in the optional field and the calculator applies it to the final discounted price for you. For the tax on its own, or to work backwards from a receipt total, use the sales tax calculator.
Percentage off against amount off
"$20 off" and "20% off" are only the same on a $100 item. Below that the fixed amount wins; above it the percentage does. On a $60 item, $20 off is a 33% discount; on a $200 item it is 10%. When a store offers a choice between a coupon and a percentage sale, the crossover is simply the amount divided by the rate — a $20 coupon beats 20% off on anything under $100.
Reading a discount honestly
- A percentage off means nothing without the reference price. Discounts are measured against a stated original, and whether that price was ever charged is a separate question — one that consumer-protection rules in several countries now regulate.
- Recovering from a discount takes a bigger percentage than the discount. Cutting $100 by 20% gives $80; getting back to $100 from there is a 25% increase, not 20%. The same asymmetry as the margin-and-markup trap.
- Buy-one-get-one-free is 50% off, and only if you wanted two. Buy-two-get-one-free is 33%.
- A discount on something you would not otherwise buy is not a saving, it is a purchase. Worth remembering during a sale.
A shopping estimate. Final prices depend on the retailer's own rounding and any local tax rules.
How this discount calculator works out its numbers
The sale price is price × (1 − discount ÷ 100). A second discount applies the same operation to that result, so the effective total is 1 − (1 − d1)(1 − d2) rather than d1 + d2. Any tax rate is applied last, to the discounted price.
- Stacked discounts are multiplied, never added. 20% then 10% is 28%, not 30%, and the calculator prints the arithmetic sum alongside so the difference is visible rather than assumed.
- Tax is applied after every discount, which is how sales tax works: it is charged on the amount actually paid.
- No rounding rules are applied beyond cents. Individual retailers round in their own way and some jurisdictions have specific tax-rounding rules, so a till receipt can differ by a cent.
- The original price is taken at face value. Whether a stated reference price was ever charged is a consumer-protection question, not an arithmetic one.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
Discount Calculator: frequently asked questions
How do I calculate a discount?
Multiply the price by (1 − discount ÷ 100). An $80 item at 30% off is $80 × 0.70 = $56.00, a saving of $24.00.
How do stacked discounts work?
They multiply rather than add, because the second cut applies to the already-reduced price. 20% off then an extra 10% off is 28% in total, not 30% — $100 becomes $80, then $72.
Is 50% off twice the same as free?
No. Half of a half is a quarter, so two 50% discounts leave you paying 25% of the original — a 75% discount. On a $100 item that is $25.
Is the discount applied before or after sales tax?
Before. Tax is charged on what you actually pay, so an $80 item at 30% off with 7.25% tax is $56.00 plus $4.06 of tax, or $60.06 total.
Is $20 off better than 20% off?
Only below $100. The two are equal at exactly $100 — below that the fixed amount is the bigger discount, above it the percentage is. Divide the coupon amount by the rate to find the crossover.
How much is 30% off $80?
$24.00 off, giving a sale price of $56.00. Add 7.25% sales tax and the till figure is $60.06.
If a price drops 20%, what increase gets it back?
25%, not 20%. $100 cut by 20% is $80, and getting from $80 back to $100 is a $20 rise on an $80 base. Percentage changes are not symmetric.
What discount is buy one get one free?
50% off, provided you actually wanted two. Buy two get one free is 33% off, and buy three get one free is 25%.