About the Coupon Stacking Calculator
When a shop is running a sale, and you also have a percentage-off coupon and a money-off voucher, it is natural to wonder what the final price will be — and whether the order in which the discounts are applied makes a difference. It does. Percentage discounts multiply rather than add, and a fixed-amount coupon is worth different amounts depending on whether it comes before or after the percentages. Stacking in the wrong order can cost several pounds or dollars on a single order.
This coupon stacking calculator combines a sale discount, a percentage coupon and a fixed-amount coupon. It shows the final price in both orders, tells you which order saves more, gives the total saving, shows the true combined percentage, and adds sales tax if you enter it.
How to Use the Coupon Stacking Calculator
Enter the price before discounts.
Enter the sale discount and the percentage coupon, as percentages.
Enter the fixed-amount coupon, such as 15 off.
Optionally, enter the sales tax rate, which is added after the discounts.
Leave any discount you do not have at zero.
How Stacked Discounts Are Worked Out
percentage factor = (1 − sale %) × (1 − coupon %)
percentages first = price × factor − fixed coupon
fixed amount first = (price − fixed coupon) × factor
with tax = best price × (1 + tax %)Step-by-Step Example
A 100 item, 20% sale, a 10% coupon and a 15-off coupon, with 8% sales tax.
Factor: 0.8 × 0.9 = 0.72 (28% off)
Percentages first: 100 × 0.72 − 15 = 57.00
Fixed first: (100 − 15) × 0.72 = 61.20
Best: 57.00, saving 4.20 more
With tax: 57.00 × 1.08 = 61.56
Total saving: 100 − 57 = 43.00 (43%)Why Percentages Multiply
The second percentage applies to a price already reduced by the first. Twenty percent off 100 leaves 80; another 10 percent off takes 8, not 10, leaving 72. So 20 percent and 10 percent together are 28 percent off, not 30. The more percentages are stacked, the bigger the gap: three discounts of 20 percent are about 48.8 percent off, not 60.
The order of the percentages does not matter — 0.8 × 0.9 is the same as 0.9 × 0.8 — but the position of a fixed amount does.
Why the Fixed Coupon Should Come Last
A fixed coupon is always worth its face value when it is applied. If it is applied first, it reduces the price the percentages work on, and so it reduces the value of the percentages. If it is applied last, the percentages work on the full price and are worth more. In the example, taking 15 off first means the 28 percent applies to 85 instead of 100, so it is worth 23.80 instead of 28.00 — exactly the 4.20 difference.
Who Decides the Order?
Usually the shop. Many online checkouts apply site-wide sales first, then percentage codes, then fixed vouchers; others apply fixed vouchers first, or allow only one code at a time. Some exclude sale items from coupons altogether, or set a minimum spend for fixed-amount vouchers, which may be measured before or after other discounts. In physical shops, staff sometimes have discretion. If the checkout lets you enter codes in different orders or on separate transactions, try both and compare.
Minimum Spend Thresholds
Fixed-amount coupons often require a minimum order, such as 15 off when you spend
- If the threshold is measured after the percentage discounts, stacking may push
your order below it. In the example, 72 after the percentages would fail a 75 minimum, even though the original price was 100. Check where the threshold is measured before relying on the saving.
Tax and Coupons
In most places, sales tax is charged on the final price after discounts. In some US states, manufacturer coupons are treated differently from store coupons and tax is charged on the price before the manufacturer's coupon. The calculator adds tax to the discounted price, which matches the most common rule.
Stacking Online and In Store
Online, stacking usually means entering a promotional code on top of a site-wide sale, sometimes with a gift card or store credit applied at the end. Gift cards and store credit are not discounts: they are a form of payment, so they come off the final price after all discounts and tax. In store, coupons are often scanned in the order they are handed over, and the till applies each one to the running total, so handing over percentage coupons before money-off vouchers can make a real difference.
Cashback on Top
Cashback from a card or website is usually calculated on the amount you finally pay, after all coupons. It is the last layer of saving, and adds a few percent to the total. The shopping savings calculator combines cashback and rewards with a sale price, if you want to include them too.
Understanding Your Result
Best final price is the lowest price, with tax if entered.
Each order shows the price with percentages first and with the fixed amount first.
Best order tells you which order to use and how much it saves.
Total saving gives the saving in money and as a percentage.
Combined percentages shows the true combined percentage discount.
Worth knowing reminds you to check each coupon's terms.
When Should You Use This Calculator?
Shopping during a sale with extra coupons.
Checking a checkout total is right.
Deciding whether a fixed or percentage voucher is better.
Comparing two shops' stacked offers.
Understanding why stacked percentages save less than expected.
Common Mistakes
Adding percentage discounts together.
Applying the fixed coupon first when you have a choice.
Missing a minimum spend after other discounts.
Assuming every coupon can be combined.
Forgetting tax in the final total.