Discount Calculator
To find a sale price, multiply the price by 1 minus the discount as a decimal: $80.00 with 20% off is $64.00, a saving of $16.00. Stacked discounts multiply instead of adding: 20% off and then an extra 15% off the reduced price is 32% off in total, not 35%, so $80.00 costs $54.40 and you save $25.60. Sales tax comes after the discount, so a 7.5% tax adds $4.08 for a total of $58.48 (the rate is only an example). Buy one get one at 50% off works out to 25% off each item, and the calculator also works backwards from a sale price to the original price. Amounts are exact to the cent: the price after all discounts is worked out exactly and rounded once, half up.
Updated Runs in your browser: nothing you enter is uploadedHow this tool works
Sale price $54.40
$80.00 with 20% off and then an extra 15% off is $54.40: you save $25.60, an effective 32% off. With 7.5% sales tax on the discounted price, the total is $58.48.
- Original price
- $80.00
- 20% off
- $16.00
- Extra 15% off
- $9.60
- You save
- $25.60
- Effective discount
- 32%
- Sale price
- $54.40
- Sales tax (7.5%) on the discounted price
- $4.08
- Total with tax
- $58.48
Sale price at common discounts
| Original price | 10% off | 15% off | 20% off | 25% off | 30% off | 50% off |
|---|---|---|---|---|---|---|
| $20.00 | $18.00 | $17.00 | $16.00 | $15.00 | $14.00 | $10.00 |
| $50.00 | $45.00 | $42.50 | $40.00 | $37.50 | $35.00 | $25.00 |
| $80.00 | $72.00 | $68.00 | $64.00 | $60.00 | $56.00 | $40.00 |
| $100.00 | $90.00 | $85.00 | $80.00 | $75.00 | $70.00 | $50.00 |
| $250.00 | $225.00 | $212.50 | $200.00 | $187.50 | $175.00 | $125.00 |
Stacked discounts: the effective total
| First discount | Extra discount | Adding them (wrong) | Effective discount | Sale price for $100.00 |
|---|---|---|---|---|
| 10% | 10% | 20% | 19% | $81.00 |
| 20% | 10% | 30% | 28% | $72.00 |
| 20% | 15% | 35% | 32% | $68.00 |
| 25% | 25% | 50% | 43.75% | $56.25 |
| 30% | 20% | 50% | 44% | $56.00 |
| 40% | 10% | 50% | 46% | $54.00 |
| 50% | 20% | 70% | 60% | $40.00 |
Buy X get Y: the effective discount per item
| Deal | Items per group | Effective discount per item | Cost of one group at $20.00 each |
|---|---|---|---|
| Buy 1 get 1 free | 2 | 50% | $20.00 |
| Buy 1 get 1 at 50% off | 2 | 25% | $30.00 |
| Buy 1 get 1 at 25% off | 2 | 12.5% | $35.00 |
| Buy 2 get 1 free | 3 | ≈ 33.3333% | $40.00 |
| Buy 2 get 1 at 50% off | 3 | ≈ 16.6667% | $50.00 |
| Buy 3 get 1 free | 4 | 25% | $60.00 |
| Buy 1 get 2 free | 3 | ≈ 66.6667% | $20.00 |
Working back to the original price
| Sale price | Discount | Original price | You saved |
|---|---|---|---|
| $60.00 | 25% | $80.00 | $20.00 |
| $35.20 | 20% | $44.00 | $8.80 |
| $89.99 | 10% | $99.99 | $10.00 |
| $12.75 | 15% | $15.00 | $2.25 |
| $150.00 | 50% | $300.00 | $150.00 |
How to calculate a discount
- Choose what you want to work out. Pick “Sale price” for the price after a discount, “Buy X get Y” for deals like buy one get one, or “Original price” to work back from a sale price.
- Enter the price and the discount. Type the price ($80.00 in the example) and the discount, either as a percentage or as an amount off. 20% off is $64.00.
- Add an extra discount if there is one. For “extra 15% off” on top, fill in the extra discount. It comes off the reduced price, so the total is 32%, not 35%, and the sale price is $54.40.
- Add sales tax if you want the total. Enter a tax rate to apply it after the discount. 7.5% on $54.40 is $4.08, a total of $58.48. Leave it blank for the discounted price alone.
- Read what you save. The result shows the sale price, the amount you save ($25.60) and the effective discount as a percentage, so deals phrased in different ways can be compared.
Frequently asked questions
- How do I calculate a percentage discount?
- Turn the percentage into a decimal, subtract it from 1 and multiply by the price. $80.00 with 20% off is $80.00 × 0.80 = $64.00, and the saving is $16.00.
- What is 20% off then an extra 15% off?
- It is 32% off in total, not 35%. The first discount leaves 80% of the price, and the extra 15% comes off that: 0.80 × 0.85 = 0.68, so you pay 68% and save 32%. On $80.00, that is $54.40, saving $25.60.
- Why are stacked discounts not added together?
- Because each discount applies to the price left by the one before. The extra 15% is taken from the already reduced price, so it is worth less than 15% of the original. Adding 20% and 15% would claim 35%, 3 points too much. For two percentages, the order does not change the total.
- How do I take a dollar amount off and then a percentage?
- Subtract the amount first, then take the percentage off what is left. On $80.00, $10.00 off and then an extra 25% off gives $52.50: you save $27.50, an effective 34.375%. The order matters when an amount is involved.
- What is the effective discount of buy one get one 50% off?
- 25% off each item. With two items at $80.00 each, the second costs half, so you pay $120.00 instead of $160.00 and save $40.00. Buy one get one free is 50% off each item.
- How does buy 2 get 1 free work out?
- In each group of three, one item is free, so each item is ≈ 33.3333% off. Three items at $80.00 cost $160.00 instead of $240.00. If you buy only some of a group, such as four items, the leftover items are not discounted, and the calculator accounts for that.
- Is sales tax charged before or after the discount?
- Usually after: tax is charged on the price you pay, so the discount lowers the tax too. $54.40 at 7.5% tax is $4.08, for $58.48. Some coupons and some places treat tax differently (for example, a manufacturer’s coupon may not reduce the taxable price), so check the rules where you shop. The 7.5% here is only an example rate.
- How do I find the original price from the sale price?
- Divide the sale price by 1 minus the discount as a decimal. $54.40 after 20% off and an extra 15% is $54.40 ÷ 0.68 = $80.00. Adding 32% to the sale price instead would overshoot, because the discount was a share of the larger original price.
- How is the result rounded?
- To the nearest cent, with half a cent rounding up. The price after all discounts is worked out from exact fractions and rounded once at the end, so the lines you see always add up to the original price.
- Is anything I type stored or sent?
- No. The calculation runs in your browser and nothing you enter leaves your device.
How it works
Prices are whole cents in integer arithmetic and every percentage is an exact fraction of what you type, so there is no floating-point error: 20% and then 15% leaves 0.8 × 0.85 = 0.68 of the price, exactly 32% off in total. The price after all discounts is computed exactly and rounded to a cent once, half up; the discount lines are the differences between those cent amounts, so the original price, the savings and the sale price always add up. A percentage discount multiplies the price by (100 − percentage) ÷ 100; an amount off subtracts the amount; an extra percentage multiplies what is left. The effective discount is 1 − (sale price ÷ original price), shown exactly when it ends in decimals and as an approximation (≈) when it does not. For buy X get Y, every group of X + Y items has Y items discounted by the stated percentage, so a full group takes Y × percentage ÷ (X + Y) off each item on average; items that do not complete a group get a discount only if they reach into the discounted positions, and the price per item is the total divided by the number of items, rounded to a cent. Sales tax, if you enter a rate, is the sale price times the rate, rounded half up, added after the discount. To work back, the original price is the sale price divided by the share left after the discounts (an amount off is added back first, in reverse order), rounded to a cent; applying the discount to that rounded price returns the sale price you entered. Everything runs in your browser and nothing you type is sent anywhere.
Sources
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