Discount Calculator
Calculate sale prices with single or stacked discounts. Factor in sales tax to see your final cost and total savings.
For stacked discounts (e.g., "extra 10% off sale prices")
Enter a price and discount to calculate savings.
How It Works
A discount is calculated by multiplying the price by the discount percentage (as a decimal) and subtracting from the original. For a 20% discount on $100: $100 × 0.20 = $20 off, final price = $80.
Stacked discounts are applied sequentially, not added together. A 20% discount followed by an additional 10% off is NOT 30% total. The second discount applies to the already-reduced price: $100 → $80 (20% off) → $72 (10% off $80). Total savings: 28%, not 30%.
Sales tax is calculated on the discounted price, not the original price. This means you pay tax only on what you actually spend, making the effective savings even better.
Frequently Asked Questions
Why do stacked discounts give less than I expect?
Each discount applies to a smaller base. 30% + 20% isn't 50% off—it's 30% off, then 20% off the reduced price. Mathematically: (1 - 0.30) × (1 - 0.20) = 0.56, meaning you pay 56% of original, saving 44%.
Does the order of discounts matter?
Mathematically, no—20% then 10% gives the same result as 10% then 20%. However, if one discount has a minimum purchase requirement or is a fixed dollar amount, order can matter. Percentage discounts are commutative.
How do I calculate price before discount?
Divide the sale price by (1 - discount percentage). If something is $80 after 20% off, original was: $80 ÷ 0.80 = $100. This is the "reverse percentage" calculation.
Is it better to apply a coupon before or after a sale?
For percentage-based discounts, order doesn't matter mathematically. For dollar-off coupons, apply them after percentage discounts to get the full dollar amount off. Store policies may dictate the order.