How to Use This Tool
Stacked discounts are the most reliably miscalculated numbers in retail, on both sides of the counter. Shoppers assume 20% plus 10% is 30%. Sellers occasionally build promotions on the same assumption and are surprised by the margin. The correct answer is 28%, and the reason is simple once you see it: the second discount is taken from a price that the first one already reduced.
Building the stack
Enter the original price, then add offers in the order the till or checkout applies them. Percentage offers work on the running total; fixed-amount offers subtract a flat sum. Order matters enormously when you mix the two — a $20 voucher applied before a 25% discount is worth $15 to you, while the same voucher applied after is worth the full $20. If a retailer's terms do not say which order they use, the step-by-step panel lets you test both in about ten seconds.
Tax placement
The tax selector handles the difference between the two systems people actually shop under. In the United States, sales tax is added at checkout to the already-discounted price, so choose after discounts. In the UK, EU and most of Asia, VAT is already inside the ticket price, so choose already in the price — the tool then shows how much of what you pay is tax, which is the figure you need for an expense claim or a VAT return.
The two percentages, and which one to quote
The true % off box is the honest figure: total saved divided by the original price. The naive sum box shows what you get by simply adding the discount percentages together, which is what the advertising implies and what a shopper does in their head. The gap between them widens quickly — three 20% discounts sum to 60% but deliver 48.8%. Neither number is a lie, but only the first one is true, and knowing the difference is worth real money on a large basket.
A note for sellers
If you are designing the promotion rather than using it, run your worst case through this tool before publishing the terms. Stackable offers that look modest individually can combine into a discount deeper than your gross margin, particularly once a fixed-amount voucher lands on a low-priced item. Setting a minimum spend on the voucher is usually the cheapest fix.
