Brex's Interchange-Driven Growth Flywheel

Brex turned startup growth into a payments revenue flywheel. YC makes money when a tiny stake becomes valuable over time, while Brex made money when a young startup that began with a free card kept hiring, buying software, traveling, and shifting more spend onto that card. Because Brex underwrote on cash and funding instead of founder credit, it could get into startups early and then collect more interchange as each customer scaled.1 2 3 4 5 6

• The model worked because startup card spend can rise much faster than headcount. A five person company might only run SaaS bills and cloud spend through the card, but after a fundraise it can add recruiting, ads, travel, contractors, and team wide employee cards. Brex kept taking a small cut every time that company swiped.1 4 5
• This was different from a normal SaaS contract. Instead of charging a fixed monthly fee, Brex effectively got a variable revenue share on customer growth. That gave it venture like exposure to the winners in its portfolio of startup customers, but through payment volume rather than equity ownership.1 3 4 6
• The tradeoff is that interchange is easy to start with but hard to defend on its own. Card programs have low switching costs, and later competitors like Ramp and software first players like Teampay pushed the market toward approvals, procurement, bill pay, and policy controls, where retention is tied to workflow instead of just the card in an employee wallet.1 5 6

The next phase of this market is turning card led distribution into full finance system ownership. The winners will still use interchange as the onramp, but the bigger outcome comes from layering software on top so revenue grows not just when customers spend more, but when finance teams run approvals, payments, accounting, and treasury in one place.1 4 5 6