Why "30% + 20% Off" Isn't 50% — Discount Stacking Math

A "30% off + 20% extra coupon" sale is not 50% off — it's exactly 44% off. Stacked discounts break consumer intuition in ways marketers exploit. Here's the math, five common traps, and a 3-second mental shortcut.

1. The Stacking Formula

Final price = Original × (1 − x/100) × (1 − y/100) Combined discount = 1 − (1 − x/100) × (1 − y/100)

2. Five Traps Consumers Fall For

① "50% off + 10% extra" feels like 60%

Actually 55%. Marketing copy often exploits the intuition gap.

② "Buy 2 Get 1" ≠ 50% off

It's 33.3% off per unit — and only if you actually want three.

③ "VAT excluded" pricing

For a standard 10% taxable sale, add 10% to a VAT-exclusive quote. A business may credit input VAT only when the purchase relates to its taxable activity, has qualifying evidence, and is not subject to a statutory exclusion; this calculator does not decide eligibility.

④ "Up to 70%"

"Up to" states the largest discount somewhere in the promotion, not the rate on every item or the item you choose. Check eligible items, coupon conditions, minimum spend, and the final checkout amount.

⑤ Card discount + coupon + points

They may stack or exclude one another under the promotion terms. Check the application order and final total before paying.

3. Stacked Discount Table

4. The 3-Second Mental Shortcut

Combined = (x + y) − (x × y / 100).
E.g., 30% + 20% → 50 − 6 = 44%. Exact.

5. Calculators

The discount tool handles one percentage discount, not automatic coupon eligibility or stacking. Calculate a combined rate using the formula above, or manually enter the first result as the next original price. The tool truncates the final price to whole won; a store's intermediate rounding or other price rules can produce a different checkout total.

• Discount Calculator — one percentage discount and final price
• VAT Calculator
• Dutch Pay Splitter