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Discount Calculator
Percent-off, fixed-off, stacked & reverse discounts — and discount-then-tax. Accurate, instant and free — for United States.
What these mean:
20% off $100.00 is $80.00 — you save $20.00.
Sale price
$80.00
You save
$20.00
Effective discount
20.00%
Set the price behind a discount with the Markup Calculator, check the margin left after a promotion with the Profit Margin Calculator, or add tax to a sale with the Sales Tax Calculator.
How a discount is calculated
A discount lowers the price you pay. A percent-off discount scales with the price; a fixed-amount discount subtracts the same dollars whatever the price. The saving is always original price − sale price.
Percent off
price × (1 − d)
sale = price × (1 − discount ÷ 100)
20% off $50 = $40 (save $10).
Fixed off
price − amount
sale = price − amount off
$10 off $100 = $90 (a 10% discount).
- 1Add sales tax after the discount: Tax is charged on the reduced price: 8% on $80 adds $6.40 for an $86.40 total — never tax the full $100 first.
- 2Take it further: Set the price behind the discount with the Markup Calculator, or check the margin a promotion leaves with the Profit Margin Calculator.
Why two discounts don't add up
When two discounts stack, each applies to the price left after the previous one, so the rates multiply rather than add. Use effective = 1 − (1 − d₁)(1 − d₂) — the combined discount is always smaller than d₁ + d₂.
| Stacked discounts | Naïve sum | Effective discount |
|---|---|---|
| 10% + 10% | 20% | 19.0% |
| 20% + 10% | 30% | 28.0% |
| 25% + 20% | 45% | 40.0% |
| 30% + 20% | 50% | 44.0% |
| 50% + 20% | 70% | 60.0% |
| 50% + 30% | 80% | 65.0% |
Finding the original price
Frequently asked questions
Sale price = original price × (1 − discount ÷ 100). A 20% discount on a $50 item is 50 × (1 − 0.20) = $40, and you save $10. The saving is simply original price − sale price.
A percent-off discount scales with the price — 20% off is $10 on a $50 item but $40 on a $200 item. A fixed-amount discount subtracts the same dollar figure regardless of price, so $10 off is a 20% discount on a $50 item but only 5% on a $200 item. On low-priced items a fixed amount is usually the bigger saving; on high-priced items a percentage usually wins.
Stacked discounts are applied one after another, each on the already-reduced price. Starting at $100, 20% off gives $80; then 10% off the $80 gives $72 — a total of 28% off, not 30%. Mathematically the two multipliers combine: (1 − 0.20) × (1 − 0.10) = 0.72. The order does not matter, and the combined discount is always smaller than adding the two rates together.
Divide the sale price by (1 − discount ÷ 100). If an item is $40 after 20% off, the original price was 40 ÷ (1 − 0.20) = 40 ÷ 0.80 = $50. This reverses a discount, which is why you cannot simply add the discount percentage back onto the sale price.
Discounts are applied first, then tax is charged on the reduced price. A $100 item at 20% off is $80, and 8% tax on $80 adds $6.40 for a $86.40 total. Charging tax on the full $100 first would overcharge you, so the discount-then-tax order always applies.
Yes — it is completely free with no sign-up, and every calculation runs entirely in your browser. Nothing you enter is sent to a server or stored.
Method, assumptions & references
Methodology: sale = price × (1 − discount/100) for percent-off; sale = price − amount for fixed-off. Stacked: effective = 1 − ∏(1 − dᵢ/100). Reverse: original = sale ÷ (1 − discount/100). Discount-then-tax: total = sale × (1 + tax/100), with the discount applied before tax. All calculations run client-side; nothing is stored.
Cross-links
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed 4 July 2026. Figures follow the methods and sources set out in our editorial standards.
Discount formulas are standard arithmetic identities. Figures are for pricing guidance only and do not account for shipping, payment fees, coupons that exclude certain items, or returns. This is not financial advice.
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