Blog / E-Commerce Tools
Published: April 10, 2026 • 9 min read • Category: E-Commerce Tools
Whether you're shopping during Black Friday, comparing prices between stores, or trying to figure out if a "20% off + extra 15% off" deal is actually better than a flat 30% off, knowing how to calculate discounts is an essential money-saving skill. This guide covers every type of discount you'll encounter, from simple percentage-off deals to complex stacked discounts and BOGO promotions.
By the end, you'll be able to quickly determine the true cost of any purchase and avoid common pricing tricks that make deals seem better than they really are.
A discount calculator is a tool that computes the final price of an item after applying one or more discounts. It calculates both the amount you save and the final price you pay. More advanced discount calculators also handle:
The most common discount type. Apply a percentage reduction to the original price:
Discount Amount = Original Price × (Discount % / 100) Sale Price = Original Price - Discount Amount Or simply: Sale Price = Original Price × (1 - Discount % / 100)
Example: A $250 jacket is 30% off.
Discount = $250 × 0.30 = $75
Sale Price = $250 − $75 = $175
Or: $250 × 0.70 = $175
A specific dollar amount is subtracted from the original price:
Sale Price = Original Price - Discount Amount
Example: $50 off a $200 item.
Sale Price = $200 − $50 = $150
Effective discount rate = ($50/$200) × 100 = 25%
When multiple discounts are applied sequentially, each discount reduces the current price, not the original. This means the total savings is always less than simply adding the percentages together.
After 1st Discount: Price₁ = Original × (1 - Discount₁) After 2nd Discount: Price₂ = Price₁ × (1 - Discount₂) Total Effective Discount = 1 - (Price₂ / Original)
Example: 20% off, then an extra 15% off. Original price: $100.
After 20% off: $100 × 0.80 = $80
After 15% off: $80 × 0.85 = $68
Total savings: $32 (effective discount: 32%, not 35%)
Common misconception: Many people think 20% + 15% = 35% off. In reality, you only save 32%. Retailers sometimes use stacked discounts because the advertised numbers look more impressive than the actual savings.
If you know the original and sale price but not the discount percentage:
Discount % = ((Original Price - Sale Price) / Original Price) × 100
Example: Was $89.99, now $67.49.
Discount = ((89.99 − 67.49) / 89.99) × 100 = (22.50 / 89.99) × 100 ≈ 25%
In most jurisdictions, sales tax is calculated on the discounted price (after the discount is applied):
Discounted Price = Original Price × (1 - Discount % / 100) Tax Amount = Discounted Price × (Tax Rate / 100) Final Price = Discounted Price + Tax Amount
Example: $150 item, 25% off, 8.5% tax.
Discounted Price = $150 × 0.75 = $112.50
Tax = $112.50 × 0.085 = $9.56
Final Price = $112.50 + $9.56 = $122.06
BOGO (Buy One Get One) deals come in several varieties:
Example: Buy 1 at $40, get 1 free.
Total for 2 items = $40
Price per item = $20 (50% off each)
Example: Buy 1 at $40, second at 50% off.
Total = $40 + $20 = $60 for 2 items
Effective discount = 25%
Example: Item A = $60, Item B = $40. BOGO Free.
Typically, you pay the higher price ($60) and get the lower-priced item free ($40).
Total = $60 for both. Savings = $40
Multiply the original price by (1 − discount percentage/100). For example, a 25% discount on $200: Sale Price = $200 × (1 − 0.25) = $200 × 0.75 = $150. You save $50.
Stacked discounts are applied sequentially, not added together. A 20% + 15% stacked discount on $100 gives: $100 × 0.80 × 0.85 = $68 (32% total savings), not $65 (35%). The second discount applies to the already-reduced price.
For a standard BOGO deal (Buy 1 Get 1 Free), you get 50% off each item when buying two. For BOGO 50% Off (Buy 1 Get 1 Half Price), the total savings on 2 items = 25%. If items have different prices, the discount typically applies to the lower-priced item.
Discount % = ((Original Price − Sale Price) / Original Price) × 100. For example, if an item was $80 and is now $60: Discount = ((80−60)/80) × 100 = 25%.
In most regions, the discount is applied to the pre-tax price. Sales tax is calculated on the discounted price. So: first apply the discount to get the sale price, then calculate tax on that sale price.
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