By default a cart can hold only one coupon. To allow stacking, switch on Can be used with other coupons on every coupon involved: a second code is accepted only if all coupons already in the cart allow stacking and the new coupon allows it too. Otherwise the customer sees "This coupon can't be used with other coupons".

When coupons are stacked, percentage discounts are added together and fixed amounts are added together. A single coupon's percentage Value is capped at 100% before being added in, but that cap is not reapplied to the combined total — stacking, say, two 60% coupons together produces a 120% computed discount, so avoid making more than one large percentage coupon stackable with another. If the stack mixes a percentage coupon with a fixed-amount coupon, the current version applies the percentage and does not additionally apply the fixed amount. Free-delivery and delivery-fee-discount flags are read from the first coupon in the cart.