Who sets the code
A merchant's MCC is assigned when it sets up card acceptance with its payment processor. The code describes the business as a whole, based on its main line of trade.
The card networks publish the code lists. Issuers then map groups of codes to their own bonus categories, such as dining, groceries or travel.
Because the store chooses its processor and describes itself, two similar businesses can end up with different codes.
Why it explains strange rewards
A supermarket code earns a grocery bonus. A superstore code does not, even for the same groceries. This is why Target and Walmart rarely earn grocery rates.
A business that sells several things can carry only one code per location or terminal. A pharmacy with a grocery aisle still codes as a pharmacy.
Most surprising rewards outcomes trace back to the code, not to a mistake by the issuer.
How to tell before you pay
The code does not appear on the receipt, and most statements show only a category label. Some issuers show the category in the transaction detail in their app.
The reliable shortcut is the store type. Supermarkets, gas stations and restaurants are predictable. Kiosks, concessions and shops inside other shops are not.
CardSwipe states the likely category alongside each recommendation, and flags cases where the code is uncertain.
