Discount Calculator
Find the sale price and your savings on any discount. Quick presets for common percentages, with optional sales tax.
Final price
The math behind a discount
Discounts are simple: take the original price, subtract a percentage, get the sale price. Sale price = Original × (1 − discount/100). The dollar savings is the difference. Easy in concept, but easy to mess up in your head when you're in a store, especially with stacked discounts and tax.
Stacked discounts compound, they don't add
Common shopping mistake: a sign reads “20% off, plus take an extra 15% off at checkout!” That sounds like 35%, but it's actually 32% — discounts stack multiplicatively, not additively.
Math: a $100 item gets 20% off = $80. Then 15% off $80 = $80 × 0.85 = $68. Total savings = $32, or 32% off. The order doesn't matter (commutative), but the result is always less than the sum of the percentages.
Rule of thumb: when stacking two discounts of x% and y%, the combined discount is (x + y − xy/100). Two 50%-offs aren't free — they're 75% off. Three 50%-offs are 87.5% off, not 150%.
When “buy one get one” is and isn't a discount
- BOGO 100% off (free) = 50% off when buying two.
- BOGO 50% off = 25% off when buying two ($100 + $50 = $150 for 2 items, vs $200 retail).
- Buy 2 get 1 free = 33% off when buying three.
- Buy 3 get 1 free = 25% off when buying four.
Worth doing only if you actually want all the items. Buying a second item you don't need to “save” on a BOGO is just spending more money.
Sales tax in the US — applied after the discount
US sales tax is collected at the point of sale, on the discounted price you actually pay. So a $100 item at 25% off in Texas (8.25% tax) costs:
- Sale price: $75
- Tax: $75 × 0.0825 = $6.19
- Final: $81.19
Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire, and Oregon. Local taxes can still apply in some of those (Alaska boroughs). See our Sales Tax Calculator for state-specific rates.
Reverse calculation: find the original price
If you see a sale price and want to know the original (or check whether the advertised discount is real):
Original = Sale price ÷ (1 − discount/100)
Example: a $40 item is “30% off.” Original = 40 ÷ 0.70 = $57.14. Don't just multiply $40 × 1.30 = $52 — that's the wrong direction. Our Percentage Calculator handles this if you want a dedicated tool for reverse percentage problems.
Spotting fake discounts (“anchor pricing”)
Some retailers inflate the “original” or “MSRP” specifically to make the discount look bigger. The actual selling price might never have been the anchor. Defenses:
- Compare across retailers — if other stores sell the same item for $60, a “was $100 now $70” deal is misleading.
- Use price history tools — CamelCamelCamel and Keepa show Amazon price history. The “new low” sometimes isn't one.
- Watch for fake urgency — “ends today” that resets daily, “only 3 left” that updates suspiciously.
- Calculate the discount from a real reference price, not the retailer's anchor.
When to act on a discount
A discount only saves you money if you would have bought the item at full price anyway. Buying something on sale that you didn't need is spending money, not saving it. Two questions to ask:
- Would I buy this at full price right now?
- If not, why is this discount changing my mind?
For genuinely needed items: discounts are real money. For impulse buys: the calculator output is a great way to see the actual cost (not the savings) before you commit.