Stacking 101: portal + card + coupon

"Stacking" sounds like a hack. It isn't. It's just knowing which rewards can be earned on the same purchase without cancelling each other out. Done in the right order, one ordinary online order can pay you from four directions. Done carelessly, one layer quietly kills another. Here's the order.

The four layers, in the order you apply them

1. Shopping-portal cashback (or miles). A shopping portal pays you cashback or miles for starting your purchase on its site. Click through one first. This is the layer with the pickiest requirements: the tracking cookie has to be set before you land on the store, so the portal click has to be the last click that lands you on the store before you check out. Other prep, like activating a card-linked offer, can happen any time beforehand; the order of the prep doesn't matter, only that nothing comes between the click-through and the purchase.
2. Your credit card's rewards. Pay with a rewards card. This layer earns on its own, independent of the other three - your card pays its usual rewards rate as long as the purchase qualifies under the card's own terms - and it never reduces what the portal pays. Portal + card is the core double-dip almost nobody should skip.
3. A card-linked offer. Amex Offers, Chase Offers, and the like, activated in your card account ahead of time. When one exists for your store it stacks on top, though it has its own tracking and its own exclusions. For how these differ from a portal click, see card-linked offers vs shopping portals.
4. A coupon at checkout. A straight discount on the price. Use the portal's own coupon, not one you found elsewhere (more on that in a second).

Get all four and a nominal "5% back" store can quietly pay double digits.

A worked example

Say you're buying from a store showing these portal rates right now:

Take the top portal rate, pay with a card earning rewards on online shopping, activate any card-linked offer for that store, and apply the portal's own coupon. Four layers, one purchase. The easiest way to lose one is pasting in an outside code, and the next section covers the rest. On the store's own page, the Best play box pairs the top portal rate with the best card from our card list (add any card-linked offer or coupon yourself); see Best Buy's page for the live version.

What breaks the stack (and how)

• Outside coupon codes. This is the classic own-goal. A code from a random coupon site can reassign the sale's commission to that site, zeroing out your portal cashback. Only use coupons the portal itself surfaces. It's one of the most common reasons cashback fails to track.
• Tabbing away after you click through. Opening another tab to price-check and buying from it can cost you the portal's tracking. Click through, then buy in the same tab.
• Excluded categories. Gift cards, some subscriptions, and third-party marketplace sellers often earn no portal cashback by rule. No amount of stacking conjures a rate that isn't being offered.

Before you stack, check the base

A tall stack on a mediocre base rate still isn't much. Check the store's current rate first, and if you're new to any of this, cashback portals 101 covers the fundamentals the stack is built on. For the card side in more depth, see does cashback stack with credit cards.