Stacked discounts don't add
A 20% discount followed by another 10% is not 30% off — it's 28% (0.8 × 0.9 = 0.72 of the original). Apply each discount to the running price, which this calculator's logic mirrors.
Reverse check
To verify a "was/now" price claim, divide the discount amount by the original price. Retail "original" prices are sometimes inflated, so the math check is the honest signal.