The “half off” that isn’t
A coat lists for $200: 30% off, then an extra 20% off the reduced price. Your brain wants to add 30 + 20 and call it 50% off. The register multiplies: you keep 70% of the price, then 80% of that. You pay 0.70 × 0.80 = 56% of $200: $112, not $100. The $12 gap is what you get when you add the two discount percents (30% + 20%) instead of multiplying the shares you still pay (70% × 80%).
Why stacked discounts mislead
Misreading a stacked promo usually means overstating the discount. The same issue shows up in tax on the discounted subtotal, subscription teaser rates, and any offer where the second percentage applies to a smaller base.
What one “percent off” does
“p% off” means: pay (100 − p)% of the current sticker. In one step: multiply the price by (1 − p/100).
Price after one discount = list × (1 − p/100) Example: 25% off $80 → $80 × 0.75 = $60
Stacking: multiply the “still paying” factors
Each new percent-off applies to the new lower number, not the original tag. Chain discounts by multiplying what you still pay after each step:
Final = L × (1 − p₁/100) × (1 − p₂/100) × …
If you add the percents instead, you invent a fake single-step discount. That is how “30 + 20” becomes a phantom 50% when reality is 44% off total.
Try it yourself
Add tax on the true subtotal before you compare merchants; “saved 40%” means nothing if shipping and fees erase it.
Expected vs guessed
Honest stack: 30% then 20% → pay 56% of list → 44% off in one breath Additive fantasy: 30 + 20 = 50 → implies pay 50% of list On $200: $112 vs $100, small until it repeats every checkout
Where you actually see this
- Clearance “extra % off”: the second cut hits the already-reduced price.
- “$15 off your first 3 months” subscriptions: annualize the dollars and compare to a plan you will keep.
- Checkout coupons on top of member pricing: sequence matters; read the receipt, not the poster.
Traps people actually fall for
- Treating the strikethrough “original” as truth; it is a reference, not an appraisal.
- Confusing “20% off the original” with “an extra 20% off the sale price”: different bases, different money.
- Letting “today only” replace a 30-second Discount calculator check. Urgency is optional; wrong bases are not.
Use the calculator
FAQ
- Is 30% off twice the same as 60% off?
No. Two successive 30%-off steps multiply: 0.7 × 0.7 = 0.49 of the original price (51% off total), not 60% off in one step.
- How do I compare two sales fast?
Convert each offer to one final multiplier on the same list price, then add tax and fees for an out-the-door total.
- Should I trust the “original price” on the tag?
Use it as context. Compare final prices on items you would actually buy, not the display price alone.