See the sale price and how much you save.
Sale price = original price × (1 − discount ÷ 100)
Discount rate = (original − sale) ÷ original × 100
The denominator is always the original price. A jacket reduced from $120 to $84 has been discounted by (120 − 84) ÷ 120 = 30 percent. Calculating against the sale price instead is a common mistake and inflates the apparent saving.
"Thirty percent off, plus an extra twenty percent at checkout" is not fifty percent off. The second reduction applies to the already-reduced price, so $120 becomes $84 and then $67.20 — an effective discount of 44 percent.
Effective rate = 1 − (1 − d₁) × (1 − d₂)
The gap widens as the individual discounts grow. Two 50% reductions produce 75% off, not 100% — nothing ever becomes free by stacking percentages. Knowing this makes it much easier to compare a single deep discount against a chain of shallower ones.
Retailers frequently present deals in a form that obscures the actual saving. Converting to a percentage makes comparison trivial.
If you only need one item, a straight 40% discount beats every offer on that list. The multi-buy is better only when you would genuinely have bought the extra units anyway and they will not go to waste.
A large percentage means nothing if the reference price was inflated. "Was $300, now $90" and "was $100, now $90" cost you exactly the same. Consumer protection rules in many countries require that a "was" price must have been genuinely charged for a meaningful period, but enforcement varies.
The reliable check is the price history of the specific item rather than the advertised reduction. Comparing against what the same product costs elsewhere today tells you more than any percentage on the label.