Discount Calculator
Calculate sale prices, savings, and final price with tax.
This discount calculator takes a list price and a percentage off and returns the sale price, the amount saved, and the final price with tax added back. It also works backwards from a sale price to the original.
The number on the tag is rarely the number you pay. A 20% discount plus 8% sales tax lands at 86.4% of the list price, not 80% — and two discounts of 20% and 10% are 28% off, not 30%. Below: the formula, the stacking trap, and the order in which discounts and tax apply.
How to calculate a discount
- Convert the discount to a decimal: 20% → 0.20.
- Sale price = list × (1 − 0.20) = 80 × 0.80 = $64.
- Savings = list − sale price = $16.
- Add tax last: final = 64 × 1.08 = $69.12.
- To reverse it, divide: a $64 sale price after 20% off means the original was 64 / 0.80 = $80.
Example
A $120 jacket at 30% off is $84, a saving of $36. With 8.5% sales tax the register total is $91.14. If the tag instead says $84 after 30% off and you want to know the original, divide: 84 / 0.70 = $120. Adding 30% back to $84 gives $109.20, which is wrong — that is the reverse-percentage trap.
Discount formula
Sale price = list × (1 − d/100). Savings = list × d/100. Final with tax = sale price × (1 + t/100). Original from sale price = sale / (1 − d/100).
How to use this calculator
- Enter the price before any discount.
- Set the discount percentage — the field accepts decimals, so 12.5 works.
- Add the sales tax rate if you want the out-of-pocket total; leave it at 0 to see the pre-tax price.
- Read the sale price and the savings line. For a second discount, apply it to the sale price, not the original.
Stacked discounts do not add
20% off then an extra 10% is not 30% off. The second discount applies to the already-reduced price: 100 → 80 → 72, a total of 28%. The general rule is (1 − a)(1 − b) − 1, so 20% and 10% combine to −28%, and 30% and 20% combine to −44%.
Discount before or after tax
In most jurisdictions the discount applies to the pre-tax price, then tax is charged on the reduced amount. That ordering is worth money: on a $120 item at 30% off with 8.5% tax, discounting first costs $91.14, while taxing first and discounting after costs $91.14 only if the tax is also discounted — otherwise you pay $2.55 more.
Discount, markdown, and coupon
A discount is taken off the current price; a markdown is a permanent reduction in the list price; a coupon is a separate instrument applied at checkout and sometimes taxed differently. Two 20% coupons may also be capped, or one may apply only to full-price items.
What this calculator leaves out
Minimum spend thresholds, category exclusions, loyalty pricing, and return windows. A 40% discount on an item you would not have bought at full price is not a saving — it is a purchase.
Common mistakes
- Adding stacked percentages. 20% then 10% is 28% off, not 30%.
- Adding the discount back to find the original price. $84 after 30% off means $120, not $109.20.
- Ignoring the tax base. Discounting before tax and discounting after tax give different totals.
FAQ
How do I calculate 20% off?
Multiply the price by 0.8. A $60 item becomes $48, and you save $12.
What is 30% off $80?
$56. Multiply 80 by 0.7, or take 30% ($24) off the price.
Do two discounts of 20% equal 40% off?
No. They compound to 36% off: 100 → 80 → 64. The second 20% applies to the reduced price, so the saving is smaller than it looks.
Is the discount applied before or after tax?
Usually before. Tax is charged on the discounted price, which is why a 20% discount on a taxed item saves slightly more than 20% of the total.
How do I find the original price from a sale price?
Divide by (1 − discount). A $64 price after 20% off means 64 / 0.8 = $80.
What is the difference between a discount and a markdown?
A discount is a temporary reduction from the current price; a markdown is a permanent cut to the list price. Both reduce what you pay, but only the markdown changes the reference price.
How do I calculate a discount in Excel?
With price in A1 and discount in B1: =A1*(1-B1) gives the sale price, and =A1*B1 gives the saving. Format B1 as a percentage.