The economics of interchange, explained without the jargon

When a customer pays with a card, the merchant receives less than the customer paid. The difference, the merchant discount, is divided among the parties that made the transaction possible. Almost every commercial and regulatory argument in card payments is an argument about how that division should work.

The four-party model

The standard arrangement involves four participants and one intermediary:

• The cardholder, who holds an account with an issuer.
• The issuer, the bank or programme that issued the card and extends the credit or holds the funds.
• The merchant, who wants to be paid.
• The acquirer, the institution that holds the merchant's account and pays them out.
• The network, which routes authorisation and settlement between issuer and acquirer and sets the rules.

The merchant discount splits three ways. Interchange flows from the acquirer to the issuer. Scheme fees go to the network. The acquirer margin is what remains. Interchange is typically the largest component and the one set by the network rather than negotiated between the parties who pay and receive it.

Why interchange exists at all

The economic argument is that a card network is a two-sided market. Issuing costs money (fraud losses, credit losses, servicing, rewards) and issuers need a reason to promote the network's cards. Interchange transfers value from the merchant side, which benefits from card acceptance, to the issuing side, which supplies the cardholders.

The counter-argument is that because the merchant pays a rate they did not negotiate, set by a network whose incentive is to attract issuers, the rate is structurally higher than a competitive market would produce. That argument is the basis for interchange caps in several jurisdictions.

What follows from the structure

Once the mechanics are clear, a lot of otherwise puzzling behaviour becomes legible.

Rewards programmes track interchange. Where interchange is capped, generous card rewards are difficult to fund and tend to thin out. Where it is not, they flourish. Rewards are, in large part, interchange returned to the cardholder to win issuance.

Commercial and premium cards cost merchants more. They carry higher interchange rates, which is why merchants sometimes surcharge them where rules permit, and why business card portfolios are commercially attractive to issuers.

Alternative rails are pitched on cost. Account-to-account payment schemes make their argument primarily by removing interchange from the equation. Whether they succeed depends less on cost than on whether they can reproduce the parts of the card proposition merchants undervalue until they lose them: guaranteed authorisation, dispute handling, and near-universal consumer familiarity.

Chargebacks are part of the price. The dispute process merchants complain about is the consumer protection cardholders were sold. It is funded by the same fee.

Reading a merchant statement

For anyone assessing card costs, the useful exercise is to separate the three components. Interchange is largely fixed by card type and transaction characteristics. Scheme fees are fixed by the network. Only the acquirer margin is genuinely negotiable, and a blended-rate statement that does not show the split is hiding which is which.

Interchange-plus pricing, where the three components are itemised, exists precisely so a merchant can see where the money goes. Asking for it is the first step in any serious cost review.