How to Calculate Discounts and Sale Prices

A "30% off" sign is easy to read, but combined coupons and stacked discounts are trickier. This guide shows the math.

Single discount formula

Sale price = original price × (1 − discount ÷ 100). Amount saved = original price − sale price. For $80 at 30% off, sale price is 80 × 0.70 = $56 and you save $24.

Stacked discounts

When a store takes a second discount on top of the first, the second percent applies to the already reduced price, not the original. A $120 item at 25% off becomes $90. An extra 15% off $90 is $13.50 off, giving a final price of $76.50. Your total saving is $43.50, which is 36.25% of the original price and not 40%.

Why 30% plus 10% is not 40%

Take 30% off $100 to get $70. A further 10% off $70 is $7 off, leaving $63. The total discount is $37, or 37%. Two 50% discounts give 75% off, not free.

Finding the original price

If you know the sale price and the discount, divide the sale price by 1 minus the discount as a decimal. A $63 sale price after 30% off means the original was $63 ÷ 0.70 = $90. This is handy when you want to check whether a "sale" is a real discount.

Comparing deals

Percentages can mislead. Compare final prices. A 40% discount on a $100 item gives $60. A flat $35 off a $90 item gives $55, which is cheaper even though the percentage is lower (about 39%). Also compare shipping, taxes and warranty terms.

Buy one get one deals

"Buy one, get one 50% off" on two $40 items means $40 + $20 = $60 for two, a 25% saving overall. "Buy one, get one free" on two $40 items means $40 for two, a 50% saving, but only if you actually need two.

Discounts and sales tax

In most places the discount is taken before sales tax, so the tax is calculated on the lower price. A $56 sale price with 8% tax costs 56 × 1.08 = $60.48. See our guide to calculating sales tax for details.

Tips for spotting real deals

Check the price history if you can, because some "original" prices are inflated
Watch for minimum purchase rules and shipping fees
Check whether a coupon can be combined with a sale
Ask whether the discount applies before or after tax

Use the calculator

Enter the price and up to two percentages into our Discount Calculator to see the final price, the amount saved and the total discount. Our Percentage Calculator handles a single percent of any number.

Example: comparing two stores

Store A sells a jacket for $150 with 20% off, which is $120. Store B sells the same jacket for $135 with an extra 10% off, which is $121.50. The bigger percentage at Store A wins in this case, but with different starting prices the answer can change, so always compare the final prices.

Example: clearance stacking

A $60 item is marked down 40% to $36. A clearance coupon takes an extra 25% off, giving $27. The total discount is $33 off $60, which is 55%, not 65%.

Finding the percent off

If you know the original and sale prices, percent off = (original − sale) ÷ original × 100. A jacket reduced from $90 to $63 is 27 ÷ 90 = 30% off. This is useful when a store shows only the old and new price tags.

Frequently asked questions

How do I calculate 20% off quickly?

Take 10% by moving the decimal one place, double it, and subtract from the price. For $85, 10% is $8.50, 20% is $17, so the sale price is $68.