Discount Calculator

What this calculator tells you

A discount calculator shows the price you actually pay after a percentage reduction, and the amount saved. It is useful when shopping in sales, comparing offers with different percentages, or checking whether a discount on a bill or an invoice is correct.

The calculator works from the original price and the discount percentage. It shows the saving in money and the sale price, so you can judge the offer in the same terms you would pay.

How the sale price is worked out

The discount amount is the original price multiplied by the discount percentage divided by 100. The sale price is the original price minus the discount amount. Equivalently, the sale price is the original price multiplied by one minus the discount as a decimal. The two methods always give the same answer, so you can use whichever is easier to check by hand.

A worked example

Suppose an item costs 80 and is reduced by 25%. The discount is 80 multiplied by 25% and divided by 100, which is 20. The sale price is 80 minus 20, which is 60. Checking the other way, 80 multiplied by 0.75 also gives 60. The saving is 20, and the price falls by a quarter.

Common pitfalls with percentage discounts

Two successive discounts do not add up. A 20% reduction followed by a further 20% reduction leaves 80% of 80%, which is 64% of the original price, a total discount of 36%, not 40%. Retailers sometimes advertise combined offers, so check whether the second discount applies to the reduced price.

A percentage reduction is also not the same as a percentage increase in reverse. After a 25% discount, the price must rise by one third of the sale price, not by 25%, to get back to the original. Keep this in mind when comparing a discount with a later price rise.

What the calculator leaves out

Sales tax or value-added tax may be charged on the discounted price, and the rule for when tax applies differs by country and product. Delivery charges, service fees and minimum spend conditions are also not included. Read the full terms of any offer before assuming the reduced figure is the final amount you pay.

Comparing deals of different kinds

A percentage discount, a fixed amount off and a buy-one-get-one offer can all describe the same saving in different ways. Convert each to a price per unit or a final cost for the quantity you need, and compare those figures. The offer with the largest percentage is not always the cheapest.

Check whether the discount applies to the full price or to a reduced price after a previous discount, and whether it applies to every item in the range or only selected ones. These conditions often decide whether the saving is real.

Using the result

Use the calculator to check whether a sale is as large as advertised, to compare discounts on different items, and to work out a target price for a purchase. If you need a discount of a certain amount, divide the saving you want by the original price to find the percentage needed.

Working out the price before the discount

Sometimes you know the sale price and want the original, or you know the saving in money and want the percentage. To find the original price from a sale price, divide the sale price by one minus the discount as a decimal. For example, 60 after a 25% discount gives an original of 80. Use the same approach to check a discount on an invoice, so you can see whether the reduction was applied correctly.