To calculate a discount, multiply the original price by the discount percentage and subtract the result from the price. For 30% off $79.99, the discount is $24.00 and the sale price is $55.99. The shortcut is to multiply the price by what you still pay: 79.99 × 0.70 = $55.99.
Our free discount calculator shows the amount you save and the final price as soon as you set the percentage. This guide covers the formula, mental math for the shop floor, how stacked discounts really work, and how to find the discount when you only know two prices.
The discount formula
Discount amount = Original price × (Discount % ÷ 100)
Sale price = Original price × (1 − Discount % ÷ 100)Worked example: 30% off $79.99
- Convert the percentage to a decimal: 30 ÷ 100 = 0.30.
- Discount amount: 79.99 × 0.30 = 23.997, which rounds to $24.00.
- Sale price: 79.99 − 23.997 = 55.993, which rounds to $55.99.
- Check with the shortcut: 79.99 × 0.70 = $55.99.
Common discounts on a $120 item
| Discount | You save | You pay |
|---|---|---|
| 10% off | $12.00 | $108.00 |
| 20% off | $24.00 | $96.00 |
| 25% off | $30.00 | $90.00 |
| 30% off | $36.00 | $84.00 |
| 50% off | $60.00 | $60.00 |
How to calculate percent off in your head
- 10% off: move the decimal point one place left. 10% of $120 is $12.
- 20% or 30% off: multiply the 10% figure by 2 or 3. 30% of $120 is $36.
- 25% off: divide by 4. 25% of $120 is $30.
- 50% off: divide by 2.
- Odd percentages: build them from parts. 35% is 30% plus half of 10%: $36 + $6 = $42 off $120.
How stacked discounts work
When a store offers "20% off, plus an extra 10% at checkout", the two discounts do not add up to 30%. The second discount applies to the already reduced price.
- Start at $100. After 20% off: 100 × 0.80 = $80.
- Extra 10% off: 80 × 0.90 = $72.
- Total saving: $28, which is 28% off, not 30%.
The combined discount for two percentages is 1 − (1 − a) × (1 − b). With two percentage discounts, the order makes no difference. With a fixed-amount coupon it does: on a $100 item with 20% off and a $10 coupon, taking 20% first gives $70, while applying the coupon first gives $72.
How to find the discount percentage or the original price
If you know the original and sale prices, divide the saving by the original price:
Discount % = (Original − Sale) ÷ Original × 100A jacket marked down from $60 to $42 has a discount of 18 ÷ 60 × 100 = 30%. The percentage calculator gives the same answer in its Percentage Change panel, as −30%.
To work backward from a sale price to the original, divide by what you paid as a fraction: Original = Sale ÷ (1 − Discount % ÷ 100). A $42 item at 30% off was 42 ÷ 0.70 = $60. Our guide on how to calculate percentages covers reverse calculations in more detail.
How to use the discount calculator
- Open the discount calculator.
- Enter the Original Price, the price before any discount. It must be above zero and works in any currency.
- Set the Discount Percentage with the slider, in whole percentages from 0% to 100%, or tap a preset: 10%, 20%, 25%, 30% or 50%.
- Read the results: the Discount Amount you save and the Final Price you pay, with a note of the percentage applied.
- For stacked discounts, enter the final price as the new original price and apply the second discount.
Shopping tips and common mistakes
- Add sales tax after the discount. In the US, sales tax is generally charged on the reduced price of a store discount, though rules for manufacturer coupons vary by state. A $120 item at 25% off is $90; with an example 8% tax it costs $97.20. Use the sales tax calculator for the second step, and read our guide to adding and removing sales tax.
- Convert dollar-off deals to percentages. $20 off an $80 item is 25% off, which makes it easy to compare with a percentage offer elsewhere.
- Compare unit prices. A discounted large pack is only a deal if the price per item, gram or ounce is lower than the alternative.
- Check the starting price. A big percentage off an inflated "was" price can still cost more than another store's regular price.
- Tip on the full price. When a restaurant discount or voucher applies, many people tip on the pre-discount amount. The tip calculator handles that part.
Frequently asked questions
How do you calculate a discount?
Multiply the original price by the discount percentage divided by 100 to get the amount off, then subtract it from the original price. For 25% off $80, the discount is $20 and the sale price is $60.
How do I calculate 20% off a price?
Multiply the price by 0.80. For example, 20% off $45 is 45 × 0.80 = $36, a saving of $9.
Is 20% off plus an extra 10% off the same as 30% off?
No. The second discount applies to the reduced price, so 20% off followed by 10% off equals 28% off in total. A $100 item ends up at $72, not $70.
How do I find the original price before a discount?
Divide the sale price by 1 minus the discount as a decimal. An item that costs $42 after 30% off was originally 42 ÷ 0.70 = $60.
How do I calculate the discount percentage from two prices?
Subtract the sale price from the original price, divide by the original price and multiply by 100. A drop from $60 to $42 is an 18 ÷ 60 × 100 = 30% discount.
Is sales tax calculated before or after a discount?
In the US, sales tax is generally calculated on the discounted price when the store itself gives the discount. Rules for manufacturer coupons differ between states, so check your receipt or local tax guidance.