Discount Calculator guide
Work out the real price of a sale before checkout: the discounted price, how much you save, what "30% off plus an extra 20%" actually adds up to, and the final total after sales tax.
The discount formula
Sale price = original price × (1 − discount ÷ 100). Savings = original price − sale price. That is all a single discount is. 25% off means you pay 75% of the price, so multiply by 0.75. 40% off, multiply by 0.60. Once you think of a discount as "the share I still pay", mental math in a store gets much faster.
For a quick estimate, find 10% by moving the decimal point one place left, then scale. 10% of $80 is $8, so 30% is $24 and the sale price is $56.
Stacked discounts do not add up
Retailers love "take an extra 20% off sale prices" because shoppers add the numbers and think they are getting 50% off. They are not. Each discount applies to the price left after the one before it, so you multiply the shares you still pay: 0.70 × 0.80 = 0.56. You pay 56% of the original, which is 44% off.
The order does not matter, since multiplication is commutative: 20% then 30% gives the same $44.80 as 30% then 20%. What does matter is whether the second offer is a percentage or a flat dollar amount. $10 off after 30% off is not the same as 30% off after $10 off. On an $80 item, the first gives $46.00 and the second gives $49.00. When a store lets you choose, apply the percentage first and the flat-dollar coupon last.
Worked example: a sweater at checkout
A sweater lists at $80. It is marked 30% off, and you have an extra 20% off coupon. Step one: $80 × 0.70 = $56.00. Step two: $56.00 × 0.80 = $44.80. Total savings: $35.20, or 44% off.
You live in Texas, where the combined state and local rate in many cities is 8.25%. Tax applies to the discounted price: $44.80 × 1.0825 = $48.50 at the register. Enter those numbers in the calculator and all four results line up.
Sales tax and discounts in the US
In most states, sales tax is calculated on what you actually pay after store discounts. Store coupons reduce the taxable price because the retailer absorbs the cost. Manufacturer coupons are treated differently in many states because the retailer gets reimbursed, so tax is charged on the pre-coupon price.
Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire, and Oregon, though some Alaska cities charge local tax. Elsewhere, combined rates run from about 4% to over 10%. If you do not know your rate, the sales tax calculator can help, or check the receipt from a recent purchase.
Working backward
Original price from a sale price: divide by the share you paid. A $56 price tag after 30% off came from $56 ÷ 0.70 = $80. Percent off from two prices: (original − sale) ÷ original × 100. $120 marked down to $90 is 25% off.
This is useful for checking "compare at" prices. If a site claims 60% off but the item has sold for about the sale price for months, the original price was inflated. Price-history browser extensions and camelcamelcamel for Amazon show whether a discount is real.
Common mistakes
Adding stacked percentages, as above. Two discounts of 50% are 75% off, not free.
Comparing percent off instead of final price. 40% off a $150 item ($90) still costs more than 20% off a $100 item ($80). The percentage is marketing; the final price is what leaves your account.
Ignoring shipping. A 15% discount on a $40 order saves $6. If free shipping starts at $50, adding a $10 item you actually need may save more than the coupon does.
Forgetting that sales tax is not a discount problem. The calculator adds tax after the discount, which matches how US registers ring things up. If you are comparing an online price with free shipping and no tax against a local store price plus tax, compare the totals, not the sticker prices.
Frequently asked questions
How do I calculate a discount?
Multiply the price by the discount percentage and divide by 100 to get the savings, then subtract. 30% off $80 is $80 × 0.30 = $24 off, so you pay $56. Shortcut: multiply by (1 - discount), so $80 × 0.70 = $56.
Is 30% off plus an extra 20% off the same as 50% off?
No. The extra discount applies to the already-reduced price. $80 at 30% off is $56, and 20% off $56 is $44.80. That is 44% off in total, not 50%. Stacked discounts always add up to less than their sum.
Is sales tax calculated before or after the discount?
After, in almost every US state: tax applies to the price you actually pay. On a $44.80 sale price with 8.25% tax, the total is $48.50. Manufacturer coupons are the exception in many states, where tax is charged on the pre-coupon price.
How do I find the original price from the sale price?
Divide the sale price by (1 - discount). If a jacket is $56 after 30% off, the original price was $56 ÷ 0.70 = $80.
How do I calculate what percent off something is?
Divide the savings by the original price and multiply by 100. A $120 item on sale for $90 is $30 ÷ $120 = 25% off.
What is the difference between 20% off and buy one get one 50% off?
BOGO 50% off is 25% off across both items, and only if you buy two. A flat 20% off is better if you only need one, and slightly worse if you need two.
Are my numbers kept private?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.