How to calculate a discount
Sale price = original × (1 − discount ÷ 100)You save = original − sale price
A shortcut: multiply by the percentage you keep. 30% off means you pay 70%, so $120 × 0.70 = $84.
Why stacked discounts don't add up
"30% off, plus an extra 10% off" is not 40% off. The second discount comes off the already-reduced price, so the two multiply:
Final = original × (1 − 0.30) × (1 − 0.10) = original × 0.63
Paying 63% of the price means a total discount of 37%, not 40%. The order doesn't matter: 10% then 30% gives the same result.
Worked example
A $120 jacket at 30% off drops to $84.00. An extra 10% coupon takes off another $8.40, so you pay $75.60 and save $44.40 in total, which is 37% of the original price.
Shopping tips
- Compare against the usual price, not the "was" price. Some list prices are set high so the discount looks bigger.
- Check where tax is applied. In most states, sales tax is charged on the discounted price after store coupons.
- Read coupon terms. Some coupons can't be combined with sale prices, and some apply only above a minimum spend.