Stacked Discount Calculator
Compare Black Friday, Cyber Monday, student, and everyday sale offers by calculating what you will actually pay. Enter each percentage separately, choose when a fixed coupon applies, and check the total including tax and shipping. The calculator works in any single currency and does not fetch retailer offers.
How to use this calculator
Enter the merchandise price and the percentage discounts in order, separated by commas. For a double discount of 20% and 10%, enter 20, 10.
Enter any fixed coupon in the same currency and select whether the store applies it before or after percentage discounts. Check that the retailer permits stacking.
Enter tax on the discounted merchandise and shipping or other charges after tax. Compare the final checkout total and each percentage-discount step.
Formula
Apply each percentage to the remaining merchandise price: P × (1 − d1 / 100) × (1 − d2 / 100) × … . Apply the capped fixed coupon before or after those percentages, as selected. Checkout total = discounted merchandise × (1 + entered tax rate / 100) + shipping. Effective discount = merchandise savings / original merchandise price × 100.
Worked example
A price of 100 with 20% off and then another 10% off becomes 72, a 28% saving. A fixed coupon of 5 applied afterward reduces merchandise to 67. With 10% tax on that merchandise and shipping of 4, the total is 77.70.
Compare Black Friday discounts using the checkout total
Use the same eligible basket, currency, tax assumptions, and shipping charges when comparing offers. This worked example starts with merchandise priced at 100 currency units; it does not represent a current retailer offer.
1. Apply percentage discounts one after another
Enter an original merchandise price of 100 and percentage discounts of 20, 10. The first 20% discount leaves 80. The next 10% applies to 80, leaving 72: 100 × 0.80 × 0.90 = 72. The combined saving is 28%, not 30%.
For comparison, a single 30% discount leaves 70 before coupons, tax, and shipping. Compare each offer with the same starting basket; a larger displayed discount on a different reference price may still produce a higher total.
2. Check whether the fixed coupon applies before or after percentages
Add a fixed coupon of 5, tax of 10% on discounted merchandise, and shipping of 4 after tax. When the fixed coupon applies after the percentages, merchandise is 72 − 5 = 67, tax is 6.70, and checkout is 67 + 6.70 + 4 = 77.70.
Switch the fixed coupon to before the percentage discounts. Merchandise is (100 − 5) × 0.80 × 0.90 = 68.40, tax is 6.84, and checkout is 68.40 + 6.84 + 4 = 79.24. The same advertised percentages and coupon now cost 1.54 more.
3. Compare the payable amount and the offer rules
The effective merchandise discount excludes tax and shipping. Use the final checkout total to compare what you will pay, and keep the same tax rate and shipping treatment for both offers. Change them only when the actual checkout rules differ.
Check minimum spend, excluded items, coupon stacking, eligible quantities, return conditions, and the current item price. Cashback, gift-card value, buy-one-get-one offers, and jurisdiction-specific tax rules are outside this calculation; price those separately instead of entering them as another percentage discount.
| Fixed coupon order | Items | Tax | Total |
|---|---|---|---|
| No fixed coupon | 72.00 | 7.20 | 83.20 |
| 5 after percentage discounts | 67.00 | 6.70 | 77.70 |
| 5 before percentage discounts | 68.40 | 6.84 | 79.24 |
Before choosing the cheaper offer
- Compare the same eligible items and quantities using their actual prices, not only the sale headline or an assumed reference price.
- Use the retailer’s coupon order, taxable base, and shipping charges. This tool taxes discounted merchandise and adds the entered shipping amount after tax; it does not determine local tax law.
- Review the final checkout. A retailer that rounds each intermediate step, limits coupon value, or taxes shipping may differ from this estimate.
Compare your own discount stack
References for percentage discounts and total shopping costs
Assumptions and limits
- All amounts use one currency. This model retains working precision until display; a retailer that rounds at each step can charge a slightly different total.
- The tax input applies to merchandise after every discount. Shipping is added after tax; include any shipping tax in the shipping field. Some jurisdictions tax coupons differently, so this is an entered-rule estimate rather than a tax determination.
- The retailer must allow the discounts to stack. Exclusions, minimum spend, coupon caps other than the remaining price, cashback, gift cards, and buy-one-get-one promotions are not modeled. A low computed price does not verify a deal or price history.
Sources
- OpenStax: Contemporary Mathematics — Discounts, Markups, and Sales TaxPercent reductions, successive discount applications, and entered sales-tax arithmetic. Reviewed 2026-10-26.
- Federal Trade Commission: Online Shopping — Security TipsCompare total cost including shipping and add-ons, and check coupon and deal terms. Reviewed 2026-10-26.
Related calculators
Verification
How this calculator is checked
Trust comes from reproducible evidence, not model confidence. You can inspect the formula, assumptions, worked example, and cited sources on this page.
- Versioned calculationFormula logic is kept separate from the interface and covered by automated registry and behavior checks.
- Cited evidenceSources linked for independent checking: 2.
- Transparent AI useAI may assist drafting or adversarial review. Agreement between models is not proof, and no human expert review is claimed unless a named reviewer is shown.
Frequently asked questions
Is 20% off plus 10% off the same as 30% off?
No. The second percentage applies to the reduced price: 100 × 0.8 × 0.9 = 72. The combined saving is 28%, not 30%.
Does the order of coupons matter?
Percentage-only discounts give the same mathematical subtotal in any order before rounding. A fixed coupon changes the result: 100 minus 10, then 20% off is 72; 20% off first, then minus 10 is 70. Choose the order stated by the store.
Can I use this for Black Friday or double-discount sales?
Yes. Enter the actual offer terms and include tax and shipping. Compare that total with other stores and price history; this calculator does not confirm that a sale is the lowest available price.
Last updated 2026-11-08 · sequential-percent-fixed-coupon-order-tax-shipping-v1 · content-2026-11-08 · Published by YunFanLabs