Sale price in two steps
Every percent-off deal comes down to two steps: work out the saving as a percentage of the original price, then subtract it. The amount you save grows with both a higher price and a bigger discount, while the share you pay is simply 100 minus the discount percent. A 25% discount always means you pay 75% of the price.
Watching out for the real total
Sales tax is added after the discount, so the final total can sit above the marked-down price. Stacked or coupon discounts multiply rather than add, which means two 20%-off deals are not 40% off. Check the final price, tax included, so a tempting headline discount does not hide a higher total than you expected.