Key Takeaways

  • Interest-bearing installment loans generate 70% of Affirm's $50 billion in gross merchandise volume (GMV), powering the company's profitability.
  • Shorter-term pay-in-four loans deliver slim Revenue Less Transaction Costs (RLTC) margins of 1% to 3%, while longer interest-bearing loans yield 4% to 6%.
  • Blended across all loan formats, Affirm maintains an industry-leading 4% RLTC margin after deducting funding costs, payment processing, and credit loss provisions.
  • Affirm acquires consumer accounts at negative customer acquisition cost (CAC) by collecting merchant fees and interest on the very first checkout transaction.

The Three Buckets Behind Affirm's Volume

Most people think buy now, pay later starts and ends with splitting a shirt into four equal payments. The public equity markets treated Affirm like a commodity lender when interest rates spiked because investors assumed short-term pay-in-four was the whole business. Fraser Christie, founder and CIO of Sandstone Global Investment, points out that Affirm runs three distinct lending engines under one hood.

“There are basically three types of offers that Affirm generates GMV from,” Christie explains. “So there's interest bearing, the 0% loans, and then the pay-in-four.”

The mechanics split sharply between these buckets. Pay-in-four and merchant-subsidized 0% loans rely on the merchant discount rate (MDR), where a seller pays Affirm a fee to close an order without charging the buyer any interest. Interest-bearing loans work differently: the shopper pays interest over 3 to 36 months, which represents 70% of Affirm's $50 billion annual GMV. By anchoring on longer-duration, high-ticket purchases, Affirm avoids competing solely in the zero-fee trench warfare where pure-play competitors fight over small transactions.

Why RLTC Is the Real Measure of Fintech Health

Fintech companies frequently publish top-line take rates to disguise deteriorating loan performance. Christie focuses instead on RLTC, or revenue less transaction costs. It shows what remains once the capital markets and delinquent borrowers take their cut.

“The gross profit or the RLTC is important because it captures all of the revenue of the business,” Christie notes. “So the merchant discount rates, the interest, the gain on sale piece, and then nets it off against the funding costs that they're paying on their debt facilities as well as processing costs in terms of their customers paying back the loans as well as all their credit loss type costs.”

When you run the math through that filter, the products diverge. Christie observes that “those pay-in-four, those shorter term, smaller dollar value loans generate RLTC margins or gross profit margins of about 1 to 3% of GMV, whereas the interest-bearing loans generate a gross profit margin of 4 to 6%.” Blending those streams together leaves Affirm with a 4% gross profit margin on GMV. That spread protects the balance sheet against rising debt facility costs and credit shocks, giving Affirm pricing room that thin-margin payment processors cannot match.

Negative CAC as a Structural Advantage

Consumer fintech startups routinely burn half their gross margins acquiring users through paid search and social ads. Affirm bypasses that expense by integrating directly into merchant checkout flows at point of sale.

Christie outlines the unit economics of that customer acquisition: “If a customer signs up on a merchant's website, Affirm makes money on that loan and they've just won a customer. It's negative CAC for customers that come through that channel.”

Every time a shopper finances a Peloton or an airline ticket, the merchant subsidizes Affirm's distribution. Affirm gets paid an origination fee, books an immediate transaction margin, and adds a verified consumer to its database without writing a single dollar of marketing spend. Once inside the ecosystem, that consumer can be steered to the Affirm Card or repeat purchases, turning an acquisition channel into an upfront cash generator.

What to Do With This

Audit your unit economics this week by calculating your true net contribution margin after funding and default costs, not just top-line take rate. If your primary customer acquisition channel burns cash before the first sale closes, redesign your distribution so partners pay you to acquire their users at point of transaction.