Stacking rules must be complete before checkout

What it is

A coupon, a spend-threshold cut, a member rate, and a pay-method rebate can all look usable, then checkout keeps one. Complete stacking rules means, before the order is pushed to pay, saying which combine, the priority, the cap, and which one remains after exclusion. It is not how strikethroughs sit, and not a comparison table missing shipping. Those are force and comparison. Here the algorithm among several offers is made explicit.

Why it happens

Each coupon says “20 off 100” at claim time; people add. Exclusion, category limits, and “best of member vs coupon” are late rules, so the math shrinks at the checkout subtotal and people think the system ate a coupon. If the rule lives only in folded terms on the claim page, it goes unread; at checkout assortment time is already sunk, so people either swallow it or leave. Completeness moves the conflict to the decision to use a coupon: the cart or checkout offer area lists “applied / unused and why,” not a single minus. Caps make face values not equal the cut; unstated caps make the arithmetic fail.

Studying it

Issue two coupons that look combinable. Compare exclusion discovered only at pay, listed in the cart, stated at claim. Watch abandon and “coupon eaten” tickets.

Independent variables: where the rule appears, whether the surviving coupon is named, whether a cap is visible. Dependent variables: checkout leave, re-assorting to hit the other coupon, predicting the actual cut.

Labs that print the rule on the sheet get it read. Live claim flows do not. Do not mix tender surcharges into the same experiment.

Where it stops holding

Auto-picking the best bundle can spare arithmetic, but unused coupons still need a why, or they look dropped. Pay-method rebates that cannot be computed in the cart must be completed at method choice, with an earlier note “extra off at pay.” Platform vs shop coupons may split internally; the user still gets one “you pay this much less.”

Applying it

• In cart or checkout offers, list each selected offer’s state: stacked, excluded unused, under threshold, plus the total cut.
• Claim pages state exclusion and cap in one sentence, not only in long terms.
• When the system swaps in a better coupon, name the one it replaced.
• Verify with two exclusive coupons: before pay, people state how much off and which went unused. Learning exclusion only at pay fails.

Related

• Within the group: H7.09.1 Discount amount needs the original price beside it · H7.09.3 Missing comparison fields read as deliberate hiding · H7.09.4 Countdown timers for limited offers must be real
• Adjacent: H7.03 Price transparency · H7.02 Checkout flow · H7.04 Payment method selection
• Search terms: coupon stacking · offer exclusivity · discount cap