Key Takeaways

  • Credit card interchange began as a merchant distribution fee, pitched to shops as an advertising channel rather than a simple transaction fee.
  • U.S. banks cross-subsidized card acquisition with airline points, creating loyalty programs that became worth strictly more than the airlines themselves.
  • Intense competition for cardholders inverted bank unit economics: borrowers in the middle of the credit score ladder are often persistently unprofitable.
  • Top-tier cardholders become profitable again only when their transaction volume is high enough for interchange fees to outrun the expense of generous rewards.

The Pitch to the Local Café

Every time you swipe a card, the merchant pays a cut called interchange. Consumers view this as a payment processing tax, but banks sold it to merchants as high-intent advertising.

Patrick McKenzie puts the original sales pitch plainly: “The sale to the café went something like this: 'You'd sell a lot more coffee if you accepted our credit cards. The best coffee drinkers carry our plastic, and they will drink coffee where they can use our plastic. You should pay us a bit for bringing you these desirable coffee drinkers, just like you'd pay an ad in the newspaper that brought you desirable coffee drinkers.' That fee is called interchange.”

Because interchange generated high gross margins on every swipe, banks suddenly had a pool of cash to acquire customers. That capital started an arms race.

The Airline Loyalty Flip

To win high-spending corporate travelers, U.S. banks stopped competing on basic card terms and started buying airline miles. They paid carriers upfront for points, then rebated interchange revenue directly to cardholders as frequent flyer rewards and cash back.

McKenzie highlights the scale of this shift: “Competition for the business of business travelers caused one of the most important innovations in both consumer banking and the travel industries ever: cross-subsidization of credit card customer acquisition with travel company loyalty points.”

This dynamic altered the airline industry balance sheet. McKenzie notes that “this economic engine became so massive, it is now worth strictly more than the airlines themselves.” United, Delta, and American stopped being transportation companies that issued credit cards. They became credit card marketing businesses that operated planes to keep the points currency liquid.

The Unprofitable Middle of the Credit Ladder

When banks rebate interchange back to consumers to win market share, the microeconomics break down in the middle tiers of credit risk.

Subprime borrowers generate profit through high interest rates and fees. Elite spenders generate profit through sheer swipe volume, paying hundreds of dollars in interchange fees every month. But borrowers in the middle of the credit score spectrum pay their balances on time, avoid interest, and optimize their points collection without spending enough to generate large interchange sums.

As McKenzie explains, “competition for desirable credit users is so intense that profit margins for banks decline midway up the credit score ladder and, for some segments, are actually persistently negative before recovering for the most desirable users, who spend so much that their interchange finally outruns the reward expense.”

Banks knowingly take negative unit economics on these users just to prevent rival institutions from capturing them. As McKenzie sums up: “Interchange makes cards so valuable that you are paid to use them.”

What to Do With This

Audit your product's rebate, discount, or referral economics this week. Check if your mid-tier customers are secretly unprofitable because the cost of your incentive programs exceeds the net margin they generate. If your retention spend assumes customers will eventually buy high-margin add-ons, test whether that cohort ever converts before subsidizing their usage.