Discount Calculator: Percentage Off & Stacked Discounts
"40% off" sounds simple until you're stacking a coupon on top of a sale price, or trying to figure out if $30 off $120 beats 25% off. A discount calculator removes the mental math, but knowing the formulas helps you spot which deal is actually better and avoid a common trap: discounts don't add up the way most people assume.
The Basic Discount Formula
Discount Amount = Original Price × (Discount % ÷ 100)
Final Price = Original Price − Discount Amount
Example: a $80 item at 25% off — Discount Amount = $80 × 0.25 = $20. Final Price = $80 − $20 = $60.
Working Backward: Finding the Discount Percentage
If you know the original and final price and want to find the percentage off:
Discount % = ((Original Price − Final Price) ÷ Original Price) × 100
Example: an item was $50, now $35. Discount % = (($50 − $35) ÷ $50) × 100 = 30% off.
Why Stacked Discounts Don't Simply Add
This is the most common discount mistake. "20% off, plus an extra 10% off" is not 30% off — the second discount applies to the already-reduced price, not the original.
| Step | Calculation | Price |
|---|---|---|
| Original price | — | $100.00 |
| After 20% off | $100 × 0.80 | $80.00 |
| After extra 10% off | $80 × 0.90 | $72.00 |
The combined effect is a 28% discount, not 30% — a $2 difference on this example, and a much bigger gap on higher-value purchases. Always calculate stacked discounts sequentially, not by adding percentages.
Discount vs. Markup: Don't Confuse Them
A discount reduces from the original price. A markup is added on top of a cost to set a selling price, and is calculated on cost — not on the final selling price. These use different bases, so a 20% markup and a 20% discount are not mirror images of each other. If you're pricing products rather than shopping, use a dedicated Margin Calculator instead, since margin and markup are also frequently confused with each other.
How to Use the Discount Calculator
- Open the Discount Calculator
- Enter the original price and the discount percentage
- View the discount amount and final price instantly
- For stacked discounts, apply the tool twice — using the first result as the new "original price" for the second discount
Frequently Asked Questions
Is 20% off then 10% off the same as 30% off?
No. Stacked percentage discounts compound rather than add, since each discount applies to an already-reduced price. The combined effect of 20% then 10% off is 28% off the original price, not 30%.
How do I calculate the original price if I only know the sale price?
Divide the sale price by (1 − discount as a decimal). For example, if an item is $60 after a 25% discount: $60 ÷ (1 − 0.25) = $60 ÷ 0.75 = $80 original price.
Does this work for calculating sales tax on a discounted price?
This calculator handles the discount only. To add tax afterward, take the discounted final price and run it through a Sales Tax Calculator — tax is generally applied to the discounted price, not the original.
