"Up to 70% off." "Buy one, get one 50% off." "Extra 30% off already-reduced items." Every one of these is a real discount and every one of them is phrased to make the math slightly harder to do in your head than it needs to be. None of it is illegal or even dishonest — it's just friction, and friction favors whoever benefits from you not finishing the calculation. Here's how to finish it anyway.
"Up to 70% off" usually means a handful of items are
The phrase is accurate but it's an upper bound, not an average. A rack advertised at "up to 70% off" might have most items at 20–30% off, with only a few clearance pieces actually hitting 70%. There's no trick here beyond reading carefully — check the tag, not the sign.
Stacked discounts don't add — they multiply
This is the one that trips people up most. If a $100 item is 30% off, then an extra 20% off on top, it is tempting to add those and assume 50% off, landing on $50. That's wrong, and it's wrong in the store's favor.
Each discount applies to the price after the previous one, not the original price:
- $100 × (1 − 0.30) = $70 after the first 30% off
- $70 × (1 − 0.20) = $56 after the extra 20% off
$56, not $50. The gap gets bigger the more discounts get stacked, which is exactly why "extra 20% off clearance" sounds more generous in a headline than it turns out to be on the receipt.
BOGO 50% is a 25% discount on the pair, not 50%
"Buy one, get one 50% off" sounds like a half-price deal. Walk through two $40 items: the first is full price at $40, the second is 50% off at $20. Total: $60 for two items that would normally cost $80. That's a real saving — 25% off the combined total — just not the 50% the headline implies on its own.
The 10-second gut check that catches all of this
Round the price to a friendly number, take 10% of it (move the decimal one place left), and scale from there. 10% of $80 is $8. So 20% is $16, 30% is $24, and 25% sits right between 20% and 30% at $20. Once you have a rough sale price in your head, compare it to what the register actually charges — if they don't match, ask why before you pay, not after.
Skip the mental math when it matters
Quick estimates are fine for a gut check, but if you're deciding between two real purchases or stacking several discounts, get the exact number instead of trusting a rough one. Our Discount Calculator handles single discounts instantly — plug in the original price and percentage, and the sale price and exact savings appear immediately, no rounding involved.