fintech rails
Buy Now, Pay Later: Who Really Pays for 'Interest-Free'?
The interest-free paradox
Here's a number that shouldn't make sense. You buy a ninety dollar pair of shoes on Klarna, split it into four payments, and the interest you pay is zero. Affirm will float you a thousand dollars for a Peloton, and charge zero percent interest. So how do companies lend out billions of dollars for free and still turn a profit? They don't, really. The loan was never free. Somebody is paying for it. It's just not always the person tapping the pay-in-four button at checkout. Once you see where the money actually comes from, the whole model snaps into focus.
Engine one: the merchant pays roughly double a card fee
Follow the fee. When you check out with a credit card, the store pays the card network roughly 2.9 percent plus thirty cents. When you check out with Klarna, the store pays up to 5.99 percent plus thirty cents. Affirm runs higher, with a take rate around 7.3 percent. So the merchant hands the Buy Now, Pay Later company close to double what a card costs them. That is the first revenue engine, and it's the big one. You pay nothing. The store quietly absorbs a fee two to three times larger than the one it already complains about. Odd thing to volunteer for. Unless the store is getting something back.
Why merchants happily pay double: conversion and basket size
So why would a store sign up to pay double? Because it sells more. Klarna's own pitch to merchants is blunt. Stores that add it report average order values jumping around 40 percent, conversion rates up about 20 percent, and shoppers coming back 46 percent more often. Run a slightly higher fee against a basket that's 40 percent bigger and bought more frequently, and the arithmetic flips in the merchant's favor. The retailer is buying volume. A few points of margin for a much larger, stickier cart is a trade most of them take without blinking. These companies aren't really selling loans to shoppers. They're selling conversion to stores.
The other three engines: interest, late fees, selling the loans
The merchant fee is one engine. There are three more. On longer plans the zero percent disappears, and Affirm charges real interest, which is now its single largest revenue line. Then there are late fees. Klarna charges seven dollars once you're more than ten days late, and across the industry late fees were over 13 percent of revenue back in 2021. And the clever one. These firms bundle up your loans and sell them to investors, booking a gain on every sale. Stack the engines together and Affirm pulled in 3.22 billion dollars in its 2025 fiscal year, up almost 40 percent. Not bad for a business that lends money for free.
Who really pays: loan stacking and phantom debt
Now the part that never makes the sales deck. The Consumer Financial Protection Bureau pulled the data in January 2025, and the picture is uneven. More than three in five of these borrowers were carrying several of these loans at the same time. A third were borrowing from more than one provider at once. The industry calls it loan stacking. Most of these loans are never reported to the credit bureaus, so nobody, not even the lenders, can see the whole pile. The polite term for that is phantom debt. Defaults are still low, around 2 percent. But the heaviest users skew subprime and already carry big balances elsewhere. For them, the free loan isn't free at all.
The takeaway: the fee never vanished, it moved
So, who actually pays for interest-free? The fee never vanished. It just moved. The merchant pays it first, then quietly prices it into what everyone pays at the register, cash and card customers included. The disciplined buyer who pays on time genuinely rides a free loan. The stretched buyer pays through stacked balances and fees. This is a 560 billion dollar market in 2025, and Klarna went public on the New York Stock Exchange in September with 114 million users. 'Interest-free' was never a gift. It's a question of who's holding the bill. Now you know where to look.
Sources
- Failory, 'Klarna's Business Model: How Do They Make Money in 2025'
- Affirm investor materials, 'The Affirm difference' (Mar 2025)
- Practical Ecommerce, 'What Merchants Should Know about Buy Now, Pay Later'
- Chargeflow, 'Klarna vs Affirm: Fees, Limits'
- Resolve, '9 Statistics Demonstrating BNPL's Effect on Conversion'
- Attrac, 'Buy Now, Pay Later for Shopify Merchants'
- Stockanalysis.com / SEC 8-K, Affirm Holdings FY2025 revenue
- Revenue Memo, 'How Klarna makes money'
- Chargeflow, 'Klarna vs Affirm'
- CFPB, 'Consumer Use of Buy Now, Pay Later' report (Jan 2025)
- CFPB newsroom, 'Heavy BNPL Use Among Borrowers with High Credit Balances'
- Payments Dive, 'Buy now, pay later users pile on debt, CFPB finds'
- Motley Fool, 'Everything Investors Need to Know About Klarna's IPO'
- Chargeflow, 'Buy Now Pay Later Market 2026 Size, Growth, Stats'
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