Discount Calculator (Percent Off + Coupon + Tax)
Stack two percent-off deals, a coupon, quantity, and sales tax to get the final price, the per-item price, and exactly how much you saved.
Discount — interactive calculator, computed instantly in your browser.
Stacking Discounts: Why 20% + 10% Is 28% Off, Not 30%
$100 → −20% → −10% → $72 (Effective 28% Off)
A discount calculator answers the question every shopper actually has: what do I pay at the register, and what did I really save? Percent-offs multiply instead of adding up, coupons come off next, and sales tax lands on the discounted subtotal. This tool runs the full chain — two percent-off deals, a coupon, quantity, and tax — and reports the final price, per-item price, and the effective discount percentage.
1. Percent-Off Chain Math
- $100 at 20% off = $80; then 10% off $80 = $72 — that is 28% effective, not 30%
- Percentages of different bases never add: the second discount applies to the already-reduced price
- Equal stacked discounts halve: two 50% offs = 75% total off, not 100%
- Order rarely matters for two percent-offs (multiplication is commutative) — it matters for coupon minimums
2. Coupons, Quantity, and Where Tax Enters
Fixed-dollar coupons subtract after percentages (most retailers sequence it that way). Quantity scales the whole order — buy-2-get-1 style offers can be modeled as an extra percent-off across units. Sales tax applies to the discounted subtotal, never the list price, in US jurisdictions; enter your local rate and the calculator shows tax as a separate line so the pre-tax savings stays visible.
3. Effective Discount vs Headline Discount
- The effective rate is the single percent-off that would have produced the same final price
- Retailers advertise each layer separately; the effective number is the one your wallet experiences
- Compare stores on effective price including tax — flash sales with deep headline rates often land within a few dollars
- Stacking caps (e.g., "one promo per order") override math, not the other way around — check the terms
4. Reverse Engineering: From Sale Price to % Off
Saw $60 tags marked down from $100? The discount is (100 − 60) ÷ 100 × 100 = 40% off. Work backwards from any two prices to compare "was/now" claims, then check whether the original was inflated before the sale — a 40% cut from a price that rose 25% last month is a 25% net move. The percentage calculator linked below handles the raw reverse-percent algebra.
🔗 Percentage Cross-References
Every discount is a percentage wearing a price tag — the raw percent math lives in our 🧮 Math Hub percentage tools.
Percent-off chains multiply, they don't add: 20% then 10% is 28% off, not 30% — the calculator prints the effective rate so checkout never surprises you.
Frequently Asked Questions (Discount)
Multiply the price by 0.80 (which is 1 − 0.20), or divide the discount amount by 100 and subtract. $100 × 0.80 = $80. For mental math, 10% is one decimal shift — double it for 20%, then subtract from the original.
No. They multiply: (1 − 0.20) × (1 − 0.10) = 0.72, so the combined effect is 28% off. The second discount applies to the reduced price, not the original — the calculator prints the effective percentage so you can compare offers honestly.
After. Sales tax applies to the final discounted subtotal in US jurisdictions, so a discount also reduces the tax you pay. The calculator applies percentage discounts first, then the coupon, then tax on the remaining subtotal to match the receipt.
Divide the sale price by the original price, subtract from 1, and multiply by 100. Paying $72 on a $100 item: 72 ÷ 100 = 0.72, so (1 − 0.72) × 100 = 28% off. The calculator reports this effective rate automatically for every price chain you enter.