A “25% off” sticker is easy enough, but sale math gets slippery when discounts stack or when you want to know your real savings at a glance. A quick method keeps you from overpaying — or overestimating the deal.
TL;DR — Enter the original price and the discount in the discount calculator; add a second discount to see the stacked price.
The basic discount
To find a sale price, multiply the original price by the discount as a decimal to get the savings, then subtract. 25% off $120 is 0.25 × 120 = $30 saved, leaving a $90 sale price. A faster route to the price directly: multiply by what is left over — 75% in this case, or 0.75 × 120 = $90.
Why stacked discounts don’t add
Here is the trap. A coupon for an extra 10% off an item already marked 25% off is not 35% off. The second discount applies to the already-reduced price, not the original. Take 25% off $120 to get $90, then 10% off that is $81 — an effective discount of about 32.5%, not 35%. Each successive discount works on a smaller base, so stacked discounts always come out a little lower than the sum.
Add tax at the end
Remember that discounts apply to the pre-tax price. To get your real checkout total, work out the sale price first, then add sales tax to that. Use the discount calculator for the sale price and savings, then the sales tax calculator for the final total.