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 honest map.

The four layers, in the order you apply them

1. Shopping-portal cashback (or miles). Click through a portal first. This is the layer with the pickiest requirements — the tracking cookie has to be set before you land on the store, so it goes first.
2. Your credit card's rewards. Pay with a rewards card. This layer is bulletproof: it earns no matter what, and it never reduces the portal's payout. 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.
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, no extra risk — as long as you don't paste in an outside code. On the store's own page we do this math for you, showing the best combined play; 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 the single most common reason cashback fails to track.
• Tabbing away after you click through. Opening a new tab to price-check, then buying from that tab, can drop the portal's cookie. 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 best rate first, and if you're new to any of this, cashback portals 101 covers the fundamentals the stack is built on.