Double Discount & Cumulative Promo Calculator

How to calculate stacked discounts and cashback correctly

Successive discounts multiply rather than add: final price = price × (1 − r1) × (1 − r2). A 30% markdown followed by a 20% coupon gives a real reduction of 44%, not 50%. Cashback is then calculated on the amount you actually pay at checkout.

The formula used by the tool

Savings are applied in this order:

1. first percentage discount on the original price: price 1 = P × (1 − r1);
2. second discount on the already reduced price, either as a percentage (price 2 = price 1 × (1 − r2)) or as a fixed voucher (price 2 = price 1 − voucher, never below €0);
3. cashback on the amount paid: net cost = price 2 × (1 − c).

The total discount shown is (P − price 2) / P. For two percentages it simplifies to r1 + r2 − r1 × r2.

Worked example

An item at €120, marked down 30%, with a 20% coupon and 5% cashback:

• after the markdown: 120 − 36 = €84;
• after the coupon: 84 − 16.80 = €67.20 to pay, a saving of €52.80 or a real discount of 44.0%;
• cashback: €3.36 credited later, for a net cost of €63.84.

Simply adding the rates (−50%) would suggest €60, which is €7.20 below the real price. With a €15 voucher instead of the coupon you pay 84 − 15 = €69, or −42.5%.

Assumptions and limits

• Two percentages give the same price in any order. A fixed voucher is worth more when it comes after the percentage; the tool always uses that order, but the retailer's terms decide the real one.
• The total discount excludes cashback, which is paid after purchase and depends on the platform's terms (validation period, cancellation on returns).
• Shipping, minimum basket and coupon caps are not modelled.
• Inputs cap the first discount at 100% and cashback at 50%.

Frequently Asked Questions

What is 30% off then 20% off as a single discount?

44%, not 50%. The second discount applies to the already reduced price: €100 becomes €70, then 70 × 0.8 = €56. The general formula is r1 + r2 − r1 × r2, so 0.30 + 0.20 − 0.06 = 0.44.

Does the order of discounts change the final price?

Not for two percentages: 100 × 0.7 × 0.8 and 100 × 0.8 × 0.7 both give €56. With a fixed voucher it does: on €120, 30% off then €15 off gives €69, while €15 off then 30% off gives €73.50.

How do I find the original price from the discounted price?

Divide the price paid by the product of the remaining factors. After 30% and 20% off, €67.20 ÷ (0.7 × 0.8) = €120. For a single 30% discount, €84 ÷ 0.7 = €120.

Is cashback included in the discount percentage?

No. The tool calculates the discount on the amount paid at checkout, then shows cashback separately on that same amount: 5% of €67.20 is €3.36, for a net cost of €63.84. Cashback is paid after a validation period and can be cancelled if you return the item.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.