Discount Calculator

Discount calculator: find the real sale price and your savings

This calculator turns an original price and a percentage off into three numbers that matter at the register: how much you save, the discounted subtotal, and the final price once sales tax is added. Below is the math behind sale pricing, how to compare deals that look similar but aren't, and the traps that make shoppers overpay.

The discount formula

Amount saved   = price × (discount% ÷ 100)
Sale subtotal  = price − amount saved
Final price    = sale subtotal × (1 + tax% ÷ 100)

Example: a $120 jacket at 25% off saves $30, dropping the subtotal to $90. With 8.25% sales tax, the out-the-door price is $90 × 1.0825 = $97.43.

Tax goes on the discounted price, not the original

A common worry is that retailers charge tax on the pre-discount price. In the vast majority of US jurisdictions they don't — tax is levied on the actual transaction amount after store discounts and coupons. (Manufacturer rebates and certain coupon types are occasional exceptions in a few states.) Applying the discount first, then tax, gives the figure that appears on your receipt.

Why stacked discounts never simply add up

"Extra 20% off already-reduced prices" sounds like 20% plus the original markdown, but percentages multiply rather than add. Each discount applies to the running total:

• $100 item, 30% off → $70
• Then an extra 20% off → $56
• Effective discount: 44% off, not 50%

To find the combined rate, multiply the remaining fractions: 0.70 × 0.80 = 0.56, meaning you pay 56% of the original and save 44%.

Comparing deals that look the same

Marketing often dresses up identical or worse deals as bargains. A few rules of thumb:

• BOGO 50% offaverages to 25% off per item — worse than a straight 50% sale if you only want one.
• "Buy 2, get 1 free" is 33% off across the three items, but only if you need all three.
• Spend-and-save thresholds("$20 off $100") are only worth it if you were going to spend near that amount anyway — otherwise you spend more to save less.

Reverse the math: from sale price to percent off

If a tag only shows the new price, you can recover the discount: subtract the sale price from the original, divide by the original, and multiply by 100. Knowing the percentage lets you compare a flat-price clearance item against a percentage-off sale on a fair footing.

Related calculators

• Percentage Calculator— percent of, percent change, and reverse-percentage math.
• Unit Price Calculator— compare cost per unit to find the genuine best buy.
• Tip Calculator— split a bill and add gratuity in seconds.