Percentage Discount Calculator

How it is calculated

The discount percentage between two prices is (original − sale) ÷ original. Going the other way, the sale price is original × (1 − discount).

The denominator is the original price, which is worth stating because the reverse calculation catches people out. A price reduced from $80 to $60 is a 25% discount, and restoring it from $60 to $80 is a 33% increase. The same movement, two different percentages, because the base changed.

A concrete case

An $80 item on sale at $60. The discount is $20 ÷ $80 = 25%.

Now stack a further 10% off the sale price. The new price is $54, and the total discount from $80 is $26 ÷ $80 = 32.5%, not 35%, because the second discount applied to $60 rather than $80.

That gap works in your favour and is worth knowing when advertising stacked offers. An extra 10% off a 25% sale is genuinely 32.5%, and describing it as 35% would be inaccurate as well as more expensive to honour.

What the number hides

Percentage discounts are perceived differently at different price points. Research on the so-called rule of 100 suggests shoppers respond better to a percentage on items under about $100 and to an absolute amount above it, $20 off a $200 item reads as larger than 10% off, despite being identical.

Discounts from an inflated reference price are also a legal issue in many jurisdictions. Advertising 40% off a price the product never genuinely sold at is regulated in the UK, EU, US and Australia, and enforcement has become more active.

Where to go from here

Present the discount in whichever form reads larger, subject to being accurate. Below $100 that is usually the percentage; above it, usually the cash amount.

Keep evidence of the reference price. Most jurisdictions require that a was-price was genuinely charged for a meaningful period before the sale, and the burden of showing it falls on the seller. A screenshot and a date is enough and is far easier to capture at the time than to reconstruct later.

Why stacked discounts compound in your favour

Sequential percentage discounts multiply rather than add, and the result is always less than the sum. Twenty percent then ten percent is 28%, not 30%. Three discounts of 20%, 10% and 5% total 31.6%, not 35%.

That is the one place discount arithmetic is kinder than intuition, and it is worth knowing for two reasons. It means a stacked offer sounds more generous than it costs, and it means a customer stacking a sale price with a code is taking less than the two numbers suggest.

The risk runs the other way, though. A stacked discount can still take the price below cost without anyone intending it, particularly where a sitewide sale and a welcome code combine on an already-discounted line. A hard price floor in the platform is the only reliable protection, because the arithmetic that prevents it is not something anyone does at checkout.