To work out a discount, multiply the price by the percentage off and divide by 100. That's your saving, and the price minus the saving is what you pay.
So a $64 pair of shoes at 15% off saves you 64 × 15 ÷ 100 = $9.60, and you pay $54.40. The trickier parts are stacked offers, working backwards, sales tax and "was" prices.
Multiply by the share you keep
A faster route skips the subtraction. At 15% off you keep 85% of the price, so multiply by 0.85: 64 × 0.85 = 54.40.
The share you keep matters most when discounts pile up, or when you work backwards.
Why 25% off plus 20% off makes 40%, not 45%
Some offers stack: a sale price first, then an extra percentage off at checkout. The second cut comes off the reduced price, not the original, so the two rates don't add up. Here's a $200 coat at 25% off, then a further 20% off:
| Offer | Applied to | Discount | You save | You pay |
|---|---|---|---|---|
| Sale price | $200 | 25% | $50 | $150 |
| Extra discount at checkout | $150 | 20% | $30 | $120 |
| One single discount, to compare | $200 | 40% | $80 | $120 |
| The sum of the two rates | $200 | 45% | $90 | $110 |
Together, you keep 0.75 × 0.80 = 0.60 of the price, which is 40% off. The gap to a true 45% is $10 on this coat. The order doesn't matter: 20% first, then 25%, also ends at $120.
Three offers? Multiply three shares. The double discount calculator runs two discounts in one go and gives the single discount that matches them.
Finding the price before the discount
A tag says $42 after 30% off, and you want the original. Adding 30% to $42 gives $54.60, which is too low. The 30% was taken from the original price, a bigger number than $42.
Divide by the share you kept instead. You kept 70%, so the original was 42 ÷ 0.70 = $60.
To get the percentage from two prices, divide the saving by the original: (60 − 42) ÷ 60 = 30%. The percentage return calculator does this too. Enter 60 and 42, and it shows a fall of 30%.
Percent off or dollars off: which saves more?
A $20 coupon and 25% off are worth the same at one price only: $80, where 25% comes to $20. Below that, the coupon wins. Above it, the percentage does.
| Price | 25% off saves | Price after 25% off | Better deal |
|---|---|---|---|
| $40 | $10 | $30 | The $20 coupon |
| $60 | $15 | $45 | The $20 coupon |
| $80 | $20 | $60 | A tie |
| $120 | $30 | $90 | 25% off |
| $200 | $50 | $150 | 25% off |
For any pair, the break-even price is the coupon divided by the rate: 20 ÷ 0.25 = 80. If the coupon needs a minimum spend, check you'd reach it anyway.
Store discounts cut the tax; manufacturer coupons may not
In California, a store's own discount lowers the tax as well as the price. The state's tax agency is the California Department of Tax and Fee Administration (CDTFA). It says a store owes tax only on what the customer pays, if no third party repays it.
Take the $200 coat in the city of Los Angeles. Its combined rate is 9.75% on the CDTFA list effective July 1, 2026:
| Case | Taxable amount | Tax rate | Sales tax |
|---|---|---|---|
| No discount | $200 | 9.75% | $19.50 |
| Store's own 25% discount | $150 | 9.75% | $14.63 |
| $50 manufacturer coupon | $200 | 9.75% | $19.50 |
Manufacturer coupons work differently. Under California's Regulation 1671.1, what the manufacturer pays the store back counts in the store's taxable receipts. By contract, the store may also charge you sales tax reimbursement on that amount.
So with a $50 manufacturer coupon, you could pay $150 plus $19.50 of tax: $169.50. After the store's own 25% off, you'd pay $150 plus $14.63, or $164.63.
That's California's rule; other states may treat coupons differently, so check yours before a big purchase. The sales tax calculator adds any rate to a discounted price.
Is the "was" price real?
A discount is only as honest as the price it starts from. The Federal Trade Commission's Guides Against Deceptive Pricing (16 CFR Part 233) deal with exactly this.
The guides say a former price "provides a legitimate basis" for a price comparison when it's genuine. The test: it was offered to the public "on a regular basis for a reasonably substantial period of time."
They give an example. A seller's regular price for a pen is $7.50, but he briefly asks $10. Then he advertises the pens as reduced from $10 to $7.50. The calculator would call that 25% off. The FTC's verdict: "This is obviously a false claim."
The guides also cover cuts "so insignificant as to be meaningless." Their example: claiming "Reduced to $9.99" when the former price was $10 "is misleading the consumer." That's a 0.1% discount.
"Buy one, get one free" is half price only if you want two
With a $30 item on a "buy one, get one free" deal, you get two for $30. That's $15 each, or 50% off, but only if you wanted a second one.
The FTC also has a guide on "free" offers, at 16 CFR Part 251. It says the word "free" indicates buyers pay "no more than the regular price" for the first item. Regular means the price of open, active sales "for a reasonably substantial period of time, i.e., a 30-day period."
So if the first item's price went up for the promotion, the "free" one isn't really free.
Sources
- eCFR, 16 CFR Part 233, Guides Against Deceptive Pricing (as of September 24, 2026)
- eCFR, 16 CFR Part 251, Guide Concerning Use of the Word "Free" and Similar Representations (as of September 24, 2026)
- CDTFA, Regulation 1671.1, Discounts, Coupons, Rebates, and Other Incentives (effective July 4, 2007)
- CDTFA, Tax Guide for Grocery Stores: Industry Topics (accessed September 26, 2026)
- CDTFA, California City & County Sales & Use Tax Rates (effective July 1, 2026)