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$89.99 at 30% off plus an extra 20% off: $50.39 — effective discount 44%, not 50%. The clearance-rack multiplication stores count on you missing.
Discounts stack by multiplying, not adding — and retailers know most shoppers add. "30% off, plus an extra 20% off" feels like half off but delivers 44%. This calculator applies stacked percents in order, adds sales tax at the end, and shows the effective discount so the real deal is visible before the register.
Shoppers use it at the clearance rack: 30% off plus an extra 20% is NOT 50% — it is 44%, $89.99 becomes $50.39, and tax gets the last word.
Because the second discount applies to the already-reduced price, not the original: $100 − 30% = $70, then −20% of $70 = $56 — you saved $44, not $50. The math: discounts multiply, 0.70 × 0.80 = 0.56, so you pay 56% and the effective discount is 44%. The gap grows with stack depth: three stacked 20% discounts are 48.8% off, not 60%. Stores design signage around the addition mistake — "extra 40% off clearance" sounds massive on an item already 50% off, but delivers 70% total, not 90%. Reverse trick worth knowing: percent-off followed by dollar-off beats the reverse order ($100 − 30% − $10 = $60 beats $100 − $10 − 30% = $63), so apply fixed coupons AFTER percent discounts when the register allows.
Three checks separate real deals from theater. First, the reference price: FTC rules require the "original" to be a genuine recent selling price, but anchor inflation is rampant — tracking tools (CamelCamelCamel for Amazon, browser price history) reveal that many "sale" prices are the everyday price. Second, the effective discount: a genuine 40%+ off is rare outside clearance and Black Friday doorbusters; typical "sales" run 10–20%. Third, the per-unit comparison: the store brand at full price often beats the name brand at 30% off. The psychological anchors are priced in: "was $199" exists to make $129 feel like winning regardless of value. The disciplined question is never "how much off?" but "is this price good for this item?" — answered by history, not signage.
Tax applies to the discounted price in most states — pay tax on $50.39, not $89.99 — but the exceptions cost money: manufacturer coupons in some states tax the PRE-coupon price, and a few states tax before store discounts too. Cross-border shopping exploits rate differences legally up to use-tax limits: Oregon (0%) vs Washington (10%+). The sneaky math: "tax included" pricing in other countries (VAT in Europe) means the sticker IS the total, which is why US prices look lower until the register. For big purchases the tax line deserves its own calculation: 8% on a $1,200 laptop is $96 — enough that the 10%-off-plus-tax-free-weekend combination (common in August back-to-school events) genuinely beats 15% off on a normal weekend.