Discounts and Sale Prices

A discount calculation has two useful results: the amount saved and the final price. Keeping them separate makes it easier to check a sale offer.

Calculate the amount saved

savings = original price × discount percentage ÷ 100

Example: A product costs 80 and is discounted by 20%. Savings = 80 × 0.20 = 16.

Calculate the final sale price

Subtract the savings from the original price. Alternatively, multiply by the percentage that remains.

sale price = original price × (1 − discount ÷ 100)

Example: 80 × (1 − 0.20) = 80 × 0.80 = 64.

This method works in any currency as long as all entered amounts use the same currency. The percentage itself has no currency.

Successive discounts

Two discounts are normally applied one after the other, not added together. The second discount uses the already reduced price as its base.

Example: Starting at 100, a 20% discount produces 80. A further 10% discount removes 8, producing a final price of 72. The combined reduction is 28%, not 30%.

remaining share = (1 − first rate) × (1 − second rate)

For 20% and 10%, the remaining share is 0.80 × 0.90 = 0.72. Therefore, 72% remains and the overall discount is 28%.

Discount followed by tax

When sales tax or VAT is added after a discount, first calculate the discounted price and then apply the tax to that new base. Whether displayed shop prices already include tax depends on the country and seller.

Example: A price of 200 receives a 15% discount, giving 170. Adding 8% tax gives 170 × 1.08 = 183.60.

Useful checks before buying

Confirm whether the percentage applies to the regular price or a previously reduced price.
Check whether delivery fees are discounted too.
For “up to” promotions, use the actual percentage on the specific item.
Compare final prices, not just the advertised discount rates.

Common mistake: Reversing a 20% discount does not mean adding 20% to the sale price. A final price of 80 after 20% off came from 100; adding 20% to 80 gives only 96.

Use the discount calculator