To calculate discount percentage, subtract the sale price from the original price, divide by the original price, and multiply by 100. A $80 item on sale for $60 is (80 − 60) ÷ 80 = 0.25, or 25% off. For a sale price, multiply by (1 − discount): $80 × 0.75 = $60.
Those two formulas cover most shopping questions. Sellers need a few more: how stacked discounts really add up (20% plus 10% is not 30%), what "buy 2, get 1 free" is worth as a percentage, how to find the original price from a sale price, and how deep a Black Friday discount can go before the sale loses money. Every example below shows the math so you can check it.
- Discount % = (original − sale) ÷ original × 100.
- Sale price = original × (1 − discount). 25% off $49.99 is $37.49.
- Original price = sale price ÷ (1 − discount). $45 after 25% off was $60.
- Stacked discounts multiply: 20% then 10% off is 28% off in total, not 30%.
- Buy 2, get 1 free is 33.3% off each item, not 50%.
How to calculate discount percentage from two prices
Divide the amount saved by the original price. That gives the discount as a decimal; multiply by 100 for a percentage.
- Find the amount saved: original price − sale price.
- Divide the amount saved by the original price (never by the sale price).
- Multiply by 100 to turn the decimal into a percentage.
| Original | Sale | Saved | Math | Discount |
|---|---|---|---|---|
| $80.00 | $60.00 | $20.00 | 20 ÷ 80 = 0.25 | 25% |
| $49.99 | $37.49 | $12.50 | 12.50 ÷ 49.99 ≈ 0.25 | 25% |
| $120.00 | $84.00 | $36.00 | 36 ÷ 120 = 0.30 | 30% |
| $35.00 | $28.00 | $7.00 | 7 ÷ 35 = 0.20 | 20% |
| $19.99 | $14.99 | $5.00 | 5 ÷ 19.99 ≈ 0.25 | 25% |
On a phone calculator, type sale ÷ original, subtract the result from 1 and multiply by 100. For $60 and $80: 60 ÷ 80 = 0.75; 1 − 0.75 = 0.25; 25%.
How do you calculate a sale price from a percentage?
Multiply the original price by what the customer still pays: 100% minus the discount. 25% off means the customer pays 75%, so multiply by 0.75.
| Discount | Multiply by | $49.99 becomes | $100 becomes |
|---|---|---|---|
| 10% off | 0.90 | $44.99 | $90.00 |
| 15% off | 0.85 | $42.49 | $85.00 |
| 20% off | 0.80 | $39.99 | $80.00 |
| 25% off | 0.75 | $37.49 | $75.00 |
| 30% off | 0.70 | $34.99 | $70.00 |
| 40% off | 0.60 | $29.99 | $60.00 |
| 50% off | 0.50 | $25.00 | $50.00 |
Prices are rounded to the cent (for example, $49.99 × 0.75 = $37.4925, shown as $37.49). Check how your store rounds before you publish a sale, since a price ending in .49 vs .50 matters for "charm" pricing. Our free discount calculator does this and the other modes below in your browser.
How do you find the original price before a discount?
Divide the sale price by (1 − discount). If something costs $45 after 25% off, the original was $45 ÷ 0.75 = $60. Don't add 25% back to $45: that gives $56.25, which is wrong because the 25% was taken from the larger, original price.
The same trap works in reverse. After a 20% markdown, you need a 25% increase to get back to the original price: $100 × 0.80 = $80, and $80 × 1.25 = $100.
How do stacked discounts work?
Stacked discounts are applied one after another, so you multiply them instead of adding them. "20% off, plus an extra 10% at checkout" works out to 1 − (0.80 × 0.90) = 0.28, or 28% off.
| Stack | Math | Total discount | $80 item becomes |
|---|---|---|---|
| 20% + 10% | 1 − 0.80 × 0.90 | 28% | $57.60 |
| 25% + 10% | 1 − 0.75 × 0.90 | 32.5% | $54.00 |
| 30% + 20% | 1 − 0.70 × 0.80 | 44% | $44.80 |
| 50% + 20% | 1 − 0.50 × 0.80 | 60% | $32.00 |
| 20% + 10% + 5% | 1 − 0.80 × 0.90 × 0.95 | 31.6% | $54.72 |
The order doesn't change the result: 10% then 20% gives the same 28%. What changes the result is whether a fixed-amount coupon (like $10 off) comes before or after a percentage discount. $10 off then 20% off an $80 item is $56; 20% off then $10 off is $54.
What percentage off is buy one, get one?
Divide the free (or discounted) value by the total number of items. The formula: discount = Y × z ÷ (X + Y), where you buy X, get Y at z% off.
| Offer | Math | Effective discount per item |
|---|---|---|
| Buy 1, get 1 free | 1 × 100% ÷ 2 | 50% |
| Buy 2, get 1 free | 1 × 100% ÷ 3 | 33.3% |
| Buy 3, get 1 free | 1 × 100% ÷ 4 | 25% |
| Buy 1, get 1 50% off | 1 × 50% ÷ 2 | 25% |
| Buy 2, get 1 50% off | 1 × 50% ÷ 3 | 16.7% |
This is why "buy one, get one 50% off" is a popular retail offer: it sounds generous but averages out at 25% off, and only if the customer buys two.
How much can I discount without losing money?
Work out the lowest price that still covers your costs and target margin, then compare it with your regular price. Lowest price = cost ÷ (1 − target margin − fee %). Deepest discount = 1 − lowest price ÷ regular price.
Example: an item sells for $49.99. It costs $18 per unit including shipping and packaging, the marketplace and payment fees total 15% of the sale price, and you want to keep a 20% margin. Lowest price = $18 ÷ (1 − 0.20 − 0.15) = $18 ÷ 0.65 = $27.69. Deepest discount = 1 − 27.69 ÷ 49.99 = 44.6%. A 40% off sale ($29.99) keeps your margin; 50% off ($25.00) doesn't.
Say a $40 item costs you $24, so you make $16. At 20% off it sells for $32 and you make $8: a 20% price cut halved the profit. To earn the same total, you need to sell twice as many units. Run your own numbers in our free profit margin calculator, and see how to calculate profit margin for the full method.
How to set Black Friday sale prices
Pick the discount from your margin first, then from what shoppers expect. Black Friday and Cyber Monday shoppers compare percentages across stores in seconds, so the number has to be clear and honest.
- Start from the deepest safe discount (above), then choose a round number below it: 20%, 25%, 30%, 40%.
- Use real reference prices. Show a "was" price only if you actually sold at it for a reasonable period. US FTC guidance on former-price comparisons and EU rules (which tie the "was" price to the lowest price in the previous 30 days) both target inflated originals. This isn't legal advice; check the rules where you sell.
- Prefer one clear discount over confusing stacks. "30% off everything" reads faster than "20% off plus an extra 10%" (which is only 28%).
- Use tiered or bundle offers (buy 2, get 1 free) to raise order value instead of cutting every item deeply.
- Account for free shipping as part of the discount cost if you add it for the sale.
- Refresh the photos. Sale traffic lands on your listing images first; a crisp main image and a seasonal lifestyle shot do more than a bigger percentage. Our guide to Black Friday product photos covers what to prepare.
Getting listings ready for a sale? Put products on clean white or seasonal backgrounds from the photos you already have, sized for each channel.
Prep sale photos7 days free · 50 credits · No credit cardFor sale banners and social graphics, AiArter's design templates include sale banner layouts you can edit with your own numbers. Our holiday listing photo checklist has the rest of the prep list.
Discount percentage formulas at a glance
| You know | You want | Formula |
|---|---|---|
| Original and sale price | Discount % | (original − sale) ÷ original × 100 |
| Original price and discount | Sale price | original × (1 − discount) |
| Original price and discount | Amount saved | original × discount |
| Sale price and discount | Original price | sale ÷ (1 − discount) |
| Two stacked discounts | Total discount | 1 − (1 − d1) × (1 − d2) |
| Cost, fee % and target margin | Lowest sale price | cost ÷ (1 − margin − fee %) |
Frequently asked questions
How do I calculate the percentage of a discount?
Subtract the sale price from the original price, divide by the original price and multiply by 100. For example, $80 reduced to $60 is $20 ÷ $80 = 0.25, which is 25% off.
How do you calculate 20% off a price?
Multiply the price by 0.80. $50 at 20% off is $50 × 0.80 = $40, and the saving is $50 × 0.20 = $10.
Is 20% off plus an extra 10% off the same as 30% off?
No. Stacked discounts multiply: 0.80 × 0.90 = 0.72, so the customer pays 72% and gets 28% off. On an $80 item that is $57.60, not $56.
How do you find the original price from a discounted price?
Divide the sale price by 1 minus the discount. A $45 price after 25% off was $45 ÷ 0.75 = $60. Adding 25% to $45 gives the wrong answer ($56.25).
What percent off is buy 2 get 1 free?
33.3%. You get three items for the price of two, so each item costs two-thirds of the full price. Buy one, get one free is 50% off, and buy one, get one 50% off is 25%.
How much should I discount for Black Friday?
There is no single right number; it depends on your margin. Work out the lowest price that keeps your target margin after costs and fees, then choose a round discount below that limit, such as 20% to 30% for many small sellers.
Turn your existing product photos into clean white, brand-color or seasonal images for every channel, with the product itself kept exactly as shot.
Start free trialSee pricing7 days free · 50 credits · No credit card. Trial images carry a small “Made with aiarter” mark; paid plans export clean files you can use commercially.
