Discount Stacking Calculator
20% off plus 10% off isn't 30% off — it's 28%, because the second discount applies to the already-reduced price. Add every coupon, threshold, multi-buy offer, and cashback deal to see what you actually pay.
How to Use the Discount Stacking Calculator
- Enter the price, quantity, and shipping, and choose whether tax is included in the price, added at checkout, or not applicable.
- Add each discount in the order your store applies them — percent off, a fixed coupon, a minimum-spend offer, a multi-buy deal, or cashback.
- Read the total: what you pay, the real discount percentage, the "stacking gap" versus the advertised sum, and whether a different order would save more.
Features
- 11 discount step types: percent off, fixed amount, capped percent, minimum-spend thresholds, price overrides, multi-buy (buy X get Y free, Nth item off), quantity discounts, and cashback
- Shows the "stacking gap" — the difference between the advertised sum of discounts and what you actually save
- Order analysis: tells you whether your order is already the best, or how much a different order would save, for the discounts where order matters
- VAT-included pricing (Denmark, Spain) or sales-tax-added pricing (US-style), plus a "doesn't reduce taxable amount" flag for manufacturer coupons
- Cashback shown separately from the checkout price, since it's paid back later, not deducted at checkout
- Step-by-step table showing the price before and after every discount, with a note when a step doesn't apply
- "Find the extra % needed" to reach a target price, and a "copy summary" button for sharing the result
- Runs entirely in your browser — no signup, no data sent anywhere
Why 20% + 10% isn't 30% off
Stacked percent discounts multiply, they don't add. Each discount applies to the already-reduced price: final = price × (1 − d₁) × (1 − d₂). A 20% discount followed by 10% gives 1 − (0.8 × 0.9) = 28% off, not 30%. On an 800 TV with 40% off plus an extra 10%, you pay 432, not 400 — a 32 "stacking gap" between what the sign implies and what you actually save.
When the order of discounts matters
With percent-only discounts, order never changes the result. It starts to matter once you mix in fixed amounts, minimum-spend coupons, price caps, or multi-buy offers. A 55 cart with a 10% discount and a "10 off orders over 50" coupon: apply the threshold coupon first and you pay 40.50; apply the percent first and the subtotal drops to 49.50 — below the 50 threshold, so the coupon no longer qualifies, and you pay 49.50 instead.
VAT included vs. sales tax added
In Denmark and Spain, VAT is already inside the shelf price, so a discount reduces the VAT too — nothing is added at the till. In the US, sales tax is normally added on top of the discounted price at checkout, though some states tax manufacturer coupons on the pre-coupon amount.
Multi-buy offers and cashback
"3 for 2" and "buy X get Y free" offers make the cheapest qualifying units free; "cashback" isn't a checkout discount at all — you pay the full discounted price and the money comes back later, so it's shown as a separate "net cost after cashback."
Know the sale price but not the original? Try the Reverse Percentage Calculator. For a single discount, use the Discount Calculator or the Percentage Calculator.
Frequently Asked Questions
Is 20% off plus 10% off the same as 30% off?
Does the order of discounts matter?
Is tax calculated before or after discounts?
How do I calculate "buy 2 get 1 free"?
Is cashback a discount?
Will the store accept my combination of discounts?
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