Discount Calculator
- You save
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- Total discount
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- Price with tax
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Checked against: 80.00 with 20% then 10% off = 57.60 (a combined 28% discount, not 30%) Last reviewed:
Sources and method
An illustration for general information, not financial advice, a quotation or an offer of credit. Figures from a lender or employer will differ.
Sale price = original price × (1 − discount ÷ 100). 20% off 80 is 80 × 0.80 = 64, a saving of 16. Two discounts multiply rather than add: 20% then 10% off is 28% in total, not 30%.
Shops advertise discounts as percentages because they are easy to print on a tag, but the figure you care about is the price at the till. This calculator gives you the sale price and the saving, combines a second discount the way retailers actually apply it, adds sales tax when you need it, and works backwards from two prices to tell you how big a discount really is.
How a discount is calculated
Saving = Original price × Discount ÷ 100
Sale price = Original price − Saving = Original price × (1 − Discount ÷ 100)
The second form is the useful one: a 35% discount means you pay 65% of the price, so multiply by 0.65. Thinking in “what I pay” rather than “what I save” also makes stacked discounts and tax straightforward.
Worked examples
A single discount
A pair of trainers priced at 120 with 35% off: 120 × 0.65 = 78. The saving is 120 − 78 = 42.
An extra discount at the till
A 250 sofa is reduced by 30%, and there is a further 10% off for opening a store card. The first discount brings it to 250 × 0.70 = 175. The second takes 10% off 175, not off 250: 175 × 0.90 = 157.50. In total you saved 92.50, which is 37% of the original — not the 40% the two numbers suggest.
Adding sales tax after the discount
The 157.50 sofa in a state with 8% sales tax costs 157.50 × 1.08 = 170.10. Because tax is charged on the discounted price, a bigger discount also means less tax.
Finding the discount from two prices
A laptop was 899 and is now 719. The saving is 180, and 180 ÷ 899 × 100 = 20.0% off. Use the “Find the discount %” tab to check whether a “huge sale” is as big as it looks.
Sale prices at a glance
| Price | 10% off | 15% off | 20% off | 25% off | 30% off | 40% off | 50% off |
|---|---|---|---|---|---|---|---|
| 10.00 | 9.00 | 8.50 | 8.00 | 7.50 | 7.00 | 6.00 | 5.00 |
| 20.00 | 18.00 | 17.00 | 16.00 | 15.00 | 14.00 | 12.00 | 10.00 |
| 25.00 | 22.50 | 21.25 | 20.00 | 18.75 | 17.50 | 15.00 | 12.50 |
| 50.00 | 45.00 | 42.50 | 40.00 | 37.50 | 35.00 | 30.00 | 25.00 |
| 75.00 | 67.50 | 63.75 | 60.00 | 56.25 | 52.50 | 45.00 | 37.50 |
| 100.00 | 90.00 | 85.00 | 80.00 | 75.00 | 70.00 | 60.00 | 50.00 |
| 150.00 | 135.00 | 127.50 | 120.00 | 112.50 | 105.00 | 90.00 | 75.00 |
| 200.00 | 180.00 | 170.00 | 160.00 | 150.00 | 140.00 | 120.00 | 100.00 |
| 500.00 | 450.00 | 425.00 | 400.00 | 375.00 | 350.00 | 300.00 | 250.00 |
Why stacked discounts never add up
When a second discount applies “on top”, it is taken from the price after the first one. So the second percentage is applied to a smaller number and saves less than it would on the original. The real combined discount is:
Combined = 1 − (1 − d₁) × (1 − d₂)
With 20% and 10%: 1 − 0.80 × 0.90 = 1 − 0.72 = 0.28, or 28%. Two 50% discounts give 75% off, not a free item.
| Discounts | Added together | Real total discount | You pay on a 100 item |
|---|---|---|---|
| 10% + 10% | 20% | 19% | 81.00 |
| 20% + 10% | 30% | 28% | 72.00 |
| 20% + 20% | 40% | 36% | 64.00 |
| 25% + 10% | 35% | 32.5% | 67.50 |
| 30% + 20% | 50% | 44% | 56.00 |
| 40% + 10% | 50% | 46% | 54.00 |
| 50% + 20% | 70% | 60% | 40.00 |
| 50% + 50% | 100% | 75% | 25.00 |
Percentage discounts can be applied in either order with the same result, because multiplication does not care about order. A fixed-amount coupon is different: take it off after the percentage discount and you save more, which is why shops usually apply it first.
Is a percentage or a fixed amount off better?
It depends on the price. A 20% discount beats 15 off on anything over 75; below that, the fixed amount wins. In general, a percentage discount of p beats a fixed discount of F when the price is more than F ÷ (p ÷ 100). When a shop offers you the choice, that one division settles it.
Common mistakes
- Adding stacked discounts. 30% + 20% is 44% off, not 50%.
- Working out the discount from the sale price. The percentage is always measured against the original price.
- Undoing a discount by adding the percentage back. A 20% discount on 100 gives 80, but adding 20% to 80 gives 96. To find the original from a sale price, divide by (1 − discount), as the reverse percentage calculator does.
- Comparing discounts without comparing base prices. 40% off an inflated “was” price can cost more than 10% off somewhere else.
Running a shop rather than shopping? A discount comes straight out of your margin — the margin and markup calculator shows what is left.
Frequently asked questions
How do I calculate a discount?
Multiply the original price by the discount as a decimal to get the saving, then subtract it. 25% off 60 is 60 × 0.25 = 15 off, so you pay 45. In one step: 60 × (1 − 0.25) = 45.
Is 20% off plus an extra 10% off the same as 30% off?
No. The second discount is taken from the already-reduced price, so the two multiply: 0.80 × 0.90 = 0.72, which is 28% off in total. On a 100 item you pay 72, not 70.
How do I work out what percentage off something is?
Subtract the sale price from the original, divide by the original and multiply by 100. Down from 120 to 90 is 30 ÷ 120 × 100 = 25% off.
Is sales tax charged on the original price or the discounted price?
In most places tax is charged on the price you actually pay, after the discount. Manufacturer coupons can be an exception in some US states, where tax is charged on the pre-coupon price. Check your local rules if the difference matters.
Does the order of two discounts matter?
Not for two percentage discounts — 20% then 10% and 10% then 20% both give 28% off. It does matter when one discount is a fixed amount: 10 off then 20% off a 100 item gives 72, while 20% off then 10 off gives 70.
What does “buy one get one half price” work out as?
Across the two items you pay 1.5 times the price for 2, which is 25% off each item. “Buy two get one free” is 33.3% off each of the three.