A tag says “30% off” — but what's the final price, and is it actually a good deal? This guide shows you how to calculate discount percentages and sale prices in seconds, handle stacked discounts correctly, and avoid the mistake almost everyone makes.
Two numbers matter in every sale: how much you save and what you pay.
saving = price × discount ÷ 100 · sale price = price − saving
Worked example: $120 jacket at 25% off.
Shortcut: sale price = price × (1 − discount ÷ 100). So $120 × 0.75 = $90 in one step.
Sometimes the tag shows old and new prices but not the percent: $120 now $90 — what percent off?
Formula: ((original − sale) ÷ original) × 100
Worked: (120 − 90) ÷ 120 × 100 = 30 ÷ 120 × 100 = 25% off. Useful for comparing “was/now” labels and checking whether a claimed discount is honest.
“Extra 10% off already-reduced items” — if an item is 20% off and you get another 10% off, is that 30% off? No.
The second discount applies to the already-reduced price:
General rule: multiply the “keep” fractions. 20% + 10% stacked = 0.80 × 0.90 = 0.72 → you pay 72%. Retailers know most shoppers just add the percentages — now you know better.
For quick in-store estimates, master 10%:
Combine with fractions for common sales: 25% = quarter off, 50% = half, 75% = pay a quarter. You'll beat the calculator to the answer most of the time.
For exact figures without the mental gymnastics, the discount calculator gives sale price and savings in one tap — and the percentage calculator handles any other percent problem.
Knowing the math also helps you see through pricing psychology:
The defense is always the same: convert every claim into actual dollars saved before deciding. Percentages are marketing; dollars are reality.
Enter the original price and discount percent to see the sale price and your exact savings instantly.
Use ((original price − sale price) ÷ original price) × 100. To get the sale price from a discount: price × (1 − discount ÷ 100).
Not 30% — the discounts multiply: 0.80 × 0.90 = 0.72, so you pay 72% (28% total off).
Find 10% by moving the decimal point one place left, then combine: 20% is double, 5% is half, 15% is 10% + 5%.
After — tax is calculated on the discounted sale price, not the original price.
Compute the discount percent from the was/now prices yourself, and compare against the item's longer-term price history if it's a big purchase.
A discount reduces the price at checkout; a rebate returns money after purchase (often by mail or app). Rebates have redemption hassle, so a smaller instant discount can be the better deal.
More free utilities on ToolKishop.