How a discount is calculated
A percentage discount multiplies the price by one minus the rate. Twenty-five per cent off $80 is 80 × 0.75 = $60, a saving of $20. Simple enough for one discount — the interesting part is what happens when two stack.
Stacked discounts do not add up
An extra 20% off an already 25%-reduced price is not 45% off. The second discount applies to the smaller number. $80 becomes $60 after 25%, then $48 after a further 20% — a total saving of $32, which is 40% off the original, not 45%. Retailers rely on "25% off, then an extra 20%" sounding larger than it is. This calculator shows the true effective discount so you can compare offers honestly.
Reading through the marketing
"Up to 70% off" means the single best item, not the rack. "Buy one get one 50% off" is 25% off across two items, not 50%. To compare deals, always look at the final price you actually pay, which is the headline figure here, rather than the percentage on the sign.
Discount then tax
Sales tax is applied after the discount, on the reduced price, so a bigger discount also lowers the tax. If you need the taxed total, take the "you pay" figure here into the sales tax calculator.