Understanding discounts
Sticker, savings, and the small print.
The math is easy. The retailer's framing is what catches you out.
The math.
Savings is sticker × percent ÷ 100. Final price is sticker minus savings, or equivalently sticker × (1 − percent/100). The two expressions agree to the last cent.
final = sticker × (1 − pct ÷ 100)
Stacked discounts don't add.
Two 25%-off coupons stacked aren't 50% off. The second discount applies to the already-reduced price. A $100 item with two 25%-offs ends up at $100 × 0.75 × 0.75 = $56.25, which is 43.75% off, not 50%. Stacking shrinks each step.
"Up to X% off."
The fine print "up to" means the deepest discount on the worst-selling item. Most of the visible inventory will be discounted far less. It's not a lie, but it's not what the banner suggests either.
Reference price tricks.
A "$200, now $80!" deal feels like a 60% saving — unless the item never sold at $200 to begin with. Reference prices set by the retailer are not the same as recent street prices. Comparison sites and price-history tools are the only honest way to see whether a "discount" is a real one.
BOGO and free shipping math.
Buy-one-get-one-free is a 50% discount averaged over two items. BOGO 50% off is a 25% discount averaged. Free shipping turns into a discount only when the order exceeds the shipping threshold; below that, the shipping was always part of the cost.