6 min read · Free educational guide
Sale price formula
Savings = original price × (discount % ÷ 100). Sale price = original − savings, or original × (1 − discount%/100).
Example: 30% off $99.99 → savings $30.00 (approximately; exact is 99.99 × 0.30), sale price ≈ $69.99.
What “% off” really means
A 25% discount multiplies the price by 0.75. You always pay (100 − discount%) percent of the original. That is why 100% off would be free, and 50% off is half price.
Stacked discounts are multiplicative
Two sequential discounts of 20% and 10% are not 30% off. After 20% off, you have 80% of the price left; then 10% off that remainder leaves 0.8 × 0.9 = 0.72, i.e. 28% total off.
Always apply discounts in the order the store states (and watch whether coupons apply to the already-reduced price).
Comparing deals fairly
Compare final out-the-door prices, not only the discount badge. Shipping, taxes, membership fees, and smaller pack sizes can erase a big “% off.” When two discounts look similar, compute both sale prices side by side.
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FAQ
- How do I calculate 15% off quickly?
- Take 10% of the price, then half of that for 5%, and add them. Subtract the sum from the original price.
- Is markdown the same as discount?
- In everyday shopping, yes: both mean reducing a price by a percent or amount. Retail accounting may use “markdown” more specifically.