How to Use the Discount Calculator

Our free discount calculator has three modes to handle any shopping scenario:

1. Simple Discount — Enter the original price, discount percentage, and optional sales tax to see your sale price, savings, and final cost.
2. Double Discount — For "additional X% off sale items" promotions. Enter both discount percentages to see the real effective discount (spoiler: 20% + 10% ≠ 30%).
3. Compare Deals — Enter two different product/discount combinations side by side to see which deal actually saves you more money.

How to Calculate Discount — The Formula

The basic discount formula is simple:

Sale Price = Original Price × (1 − Discount% ÷ 100)

Savings = Original Price − Sale Price

For double discounts, the second discount is applied to the already-discounted price, NOT the original price. This is why 20% off + 10% off = 28% total discount (not 30%).

Double Discount: Final = Price × (1 − D1/100) × (1 − D2/100)

Practical Examples

Example 1: Black Friday Sale

A $299 laptop is 25% off. Sale price = $299 × 0.75 = $224.25. You save $74.75. With 8% sales tax: $224.25 × 1.08 = $242.19 final price.

Example 2: Double Discount Trap

A $200 jacket is 30% off, plus an additional 15% off. Many shoppers expect 45% off ($110), but the actual calculation: $200 × 0.70 = $140, then $140 × 0.85 = $119. The effective discount is only 40.5%, not 45%!

Example 3: Comparing Store Deals

Store A: Headphones at $79.99 with 25% off = $59.99. Store B: Same headphones at $69.99 with 10% off = $62.99. Store A wins by $3.00! The bigger discount on the higher price beats the smaller discount on the lower price.

Frequently Asked Questions

How do I calculate 20% off a price?

Multiply the price by 0.20 to get the discount amount, then subtract from the original price. Shortcut: multiply the price by 0.80 (that's 1 minus 0.20) to get the sale price directly. For example, 20% off $75: $75 × 0.80 = $60.

Why don't double discounts add up?

Because the second discount is applied to the already-reduced price, not the original. A 20% discount followed by a 10% discount gives you (1 − 0.20) × (1 − 0.10) = 0.80 × 0.90 = 0.72, which is a 28% effective discount — not 30%.

Should I calculate the discount before or after tax?

Discounts are applied before tax. The sales tax is calculated on the discounted (sale) price, not the original price. This means you pay less tax when items are discounted.

How do I calculate the original price from a sale price?

Use the reverse formula: Original Price = Sale Price ÷ (1 − Discount%/100). For example, if an item sells for $60 after a 25% discount: $60 ÷ 0.75 = $80 original price.