Discount Calculator

How to Use the Discount Calculator

A single discount is easy. Two stacked on top of each other is where almost everyone goes wrong, because percentages multiply rather than add — and a shop advertising 25% off plus a further 15% is offering 36.25% off, not 40%.

1. Enter the original price. The price before any reduction, which in a sale is often the price the item was listed at rather than the one anybody recently paid.
2. Enter the first discount. The headline percentage, applied to the original price.
3. Enter a second discount if one applies. This is applied to the already reduced price, which is what makes the combined figure lower than the sum of the two.
4. Add a fixed-amount coupon. Money-off codes come after the percentage discounts in almost every checkout, which makes them worth more when applied to a cheaper basket, not less.
5. Set the tax rate. Tax is calculated on the discounted price, so a discount reduces the tax as well — a small extra saving that most people never notice.

The effective-discount tile is the one to read. It expresses everything — both percentages and the coupon — as a single percentage off the original price, which is the only version worth comparing between offers.

Discount Formula

Order matters. Each step operates on the result of the one before it.

The coupon behaves differently from the percentages, and in a useful way. A fixed $10 off is worth 7.8% on a $129 item and 12.2% on the $82.24 that remains after the two percentage discounts. Applying money-off codes to already discounted baskets is where they do the most work.

Example

$129 with 25% off, then a further 15%, then $10

1. After 25%: 129.00 × 0.75 = $96.75.
2. After a further 15%: 96.75 × 0.85 = $82.24. Note it is 15% of $96.75, not of $129.
3. The two percentages combined: 1 − (0.75 × 0.85) = 36.25%, not 40%.
4. After the $10 coupon: 82.24 − 10.00 = $72.24.
5. Tax at 8.25%: 72.24 × 0.0825 = $5.96.
6. Final price: 72.24 + 5.96 = $78.20. Total saved before tax: $56.76.

The effective rate

Saving $56.76 on a $129 item is an effective discount of 44.00%. Advertised as “25% off plus 15% plus $10”, it sounds larger than 40% and is in fact larger — but only because of the coupon. Without it the offer is 36.25%, which is 3.75 points less than the sum most shoppers assume they are getting.

What the discount does to tax

At full price the tax would have been 129.00 × 0.0825 = $10.64. On the discounted price it is $5.96, so the reduction saves an extra $4.68 of tax on top of the $56.76 off the goods. That is a real part of the saving in any tax-exclusive market, and it is the reason the total at the till is often slightly better than the arithmetic people do in their heads.

Why Stacked Discounts Never Add Up

Every step of the calculation, in order.

Look at the two percentage steps. The first takes $32.25 and the second, at a smaller percentage, takes $14.51 — less than half, even though 15% is more than half of 25%. That is the compounding effect in money terms, and it is why the second discount in any stacked offer is always worth less than its headline suggests.

Here is the general rule for stacked discounts, which is worth memorising because it comes up constantly:

The gap widens as the discounts get larger, which is exactly why deep stacked offers are the most misleading. A retailer advertising “up to 70% off” with a 50% sale and a further 20% code is delivering 60%, and is not technically saying anything untrue.

Four Things Worth Knowing About Discounts

Four things worth knowing about how discounts work in practice.

The original price may be notional. Reference pricing rules in many jurisdictions require the higher price to have been genuinely charged for a period, but the definitions vary and enforcement is patchy. A discount from a price nobody ever paid is arithmetic, not a saving.

Discounts and margin do not move together. A 25% price cut on a 40% margin leaves 20%, and takes half the profit. Before running an offer, check what it does to the margin and how much extra volume would be needed to stand still — usually a great deal more than the discount itself.

Order of operations differs between checkouts. Most apply percentage codes before fixed-amount ones, but not all, and some apply the coupon before tax while others apply it after. On this example the difference is small; on a large basket with a high tax rate it is not.

Free shipping is a discount too. Waiving a $6.95 delivery charge on a $129 order is a 5.4% discount that happens to be easier to advertise and easier to withdraw. Price it the same way you would price any other reduction.

There is a psychological point worth adding, because it explains why stacked offers exist at all. Two discounts announced separately read as more generous than one larger discount of the same size, even to people who know the arithmetic. A shop advertising 25% off with a further 15% at the till is offering 36.25%, and a shop advertising a flat 36.25% would be offering exactly the same thing to considerably less effect. The structure is doing work that the number is not.

The same applies to fixed-amount codes. Ten dollars off sounds specific and concrete in a way that 12.16% does not, which is why money-off codes convert well on lower-priced baskets and percentage codes work better on expensive ones. If you are designing an offer rather than evaluating one, that pairing is worth getting right: a $10 code on a $400 order is a rounding error the customer notices, and a 15% code on a $25 order gives away less than a coffee.

For the tax side of the same calculation in either direction, the sales tax calculator adds or strips tax on its own, and for the seller's view of what an offer costs, the ecommerce profit calculator shows what survives a discounted order once fees and shipping are taken out.