Shopping guide
Why 30 percent off plus 20 percent off is not 50 percent off
Why 30 percent off plus 20 percent off is not 50 percent off. Use the relevant ShopWithShery calculator to verify the math with your own prices, quantities and terms.
A 30% discount followed by 20% off the reduced price is a 44% effective discount, not 50%. A $100 item becomes $70, then $56.
The calculation to use
Effective discount = 1 − (1 − 0.30) × (1 − 0.20) = 44%Watch for: Retailers apply sequential percentage discounts to the remaining price unless the offer terms say otherwise.
A practical way to compare the offers
- Write down the price, quantity, package size and promotion exactly as shown.
- Convert both choices to the same comparison basis: per unit, delivered cost, effective discount or cost per use.
- Separate immediate checkout savings from later rewards such as cashback or store credit.
- Consider waste, required purchase quantity, recurring commitments and return restrictions.
- Choose the offer that fits both the math and the quantity you will realistically use.
Why shoppers get this wrong
Retail offers often present several numbers at once: package size, headline discount, multibuy quantity, loyalty reward and shipping threshold. Human comparison becomes difficult when those numbers use different denominators. Normalizing the offers removes much of that noise.
Calculate the real effect of discount. See both the final price and the effective savings instead of relying on the headline offer.