Discount Calculator
A "$20 off plus 15% off" sign feels generous, but the math quietly works against you. Percentage discounts compound, they don't add — so a 20% + 10% promo is really 28% off, not 30%. And when a coupon and a promo code stack, the order the checkout applies them in changes what you actually pay. Enter your original price and up to three stacked discounts below to get the true final price, total savings, and the real effective discount rate.
Enter the Price and Discounts
The Compounding Discount Formula
When two or more percentage discounts apply to the same item, the final price is the product of each remaining fraction:
Final Price = Price × (1 − d₁) × (1 − d₂) × (1 − d₃)
The effective discount rate — what you'd advertise as a single equivalent percentage — is then 100% − FinalPrice ÷ Price × 100%. Because each (1 − d) factor multiplies the previous result, stacking discounts always yields a smaller combined rate than simply adding the percentages. A 50% off rack plus an extra 30% off sounds like 80% off; it's actually 65% off (0.5 × 0.7 = 0.35 remaining).
Why Stores Love "Stacking" Language
Every "20% off your order + an extra 10% off with code SAVE" is engineered to feel like 30% off while delivering 28%. The gap seems tiny on one item, but at scale it protects margin. The same logic works in your favor when you're the seller: bundling a 10% line-item discount with a 5% cart-wide code compounds the perceived deal without compounding your cost. The calculator keeps both sides honest.
Worked Example: A $120 Jacket
A jacket is marked $120 with a 25% seasonal discount and an extra 15% loyalty coupon. The first discount drops it to $90 (75% of $120). The 15% coupon then takes 15% off $90 — that's $13.50, not $18 — leaving $76.50. You save $43.50 total, an effective discount of 36.25%, not the 40% you might assume from 25 + 15. If a third 10% clearance tier stacks on, the price falls to $68.85 (a 42.6% effective discount), again proving the percentages multiply rather than add.
Mixing Dollars and Percentages
Fixed-dollar coupons break the clean multiplication rule. On a $100 item, "10% off then $20 off" = $70, but "$20 off then 10% off" = $72. Stores almost always apply the percentage first, which leaves the fixed amount cutting a smaller base — costing you more. If you're comparing two promo stacks, run both orders through the calculator; the difference is usually a few dollars, but on a large cart it adds up.
Frequently Asked Questions
How do stacked percentage discounts work?
They multiply, not add. Each discount applies to the price remaining after the previous one, so the combined effect is always less than the sum of the percentages. The tool multiplies the (1 − d) factors for an exact final price.
Why is 20% off plus 10% off not 30% off?
The second discount hits the already-reduced price. 20% off $100 → $80; 10% of $80 is $8, so you land at $72 — a 28% discount. Retailers chain discounts because compounding understates the headline number.
How do I calculate the effective discount rate?
Divide the final price by the original to get the remaining fraction, subtract from 1, multiply by 100. Or 1 − (1−d₁)(1−d₂)(1−d₃). We show the effective rate next to the naive added rate.
Are dollar-off and percent-off discounts the same?
No. Mixing them makes order matter: percentage-first then fixed-dollar costs the shopper more. Check which order the checkout applies.
Does discount order change the final price?
Percentage discounts commute, so order doesn't matter among them. It only matters when you mix percentages with fixed-dollar amounts or capped discounts.