Apple Pay revenue hasn’t gotten much attention so far. The most valuable role Apple Pay plays for the Cupertino company is further lock-in to the ecosystem.

Once you’ve experienced the convenience of Apple Watch payments in particular, and know the security you get from the use of Apple Pay on any device, it’s not something you’ll want to give up. (Sure, there’s Google Pay and Samsung Pay too, but it still adds friction to switching platforms.)

But a news report yesterday prompted me to do some back-of-an-envelope calculations, and I reckon Apple’s mobile wallet service is rapidly headed toward becoming a multi-billion dollar revenue stream…

It was yesterday estimated that Apple Pay now accounts for a staggering 5% of global card transactions, and that the number could hit 10% by 2025.

The Financial Times reported in the run-up to launch that Apple takes a 0.15% cut on all Apple Pay transactions.

Estimating the total value of that cut involves a lot of scribbling on the backs of envelopes. But let’s try for an indicative ballpark, at least.

The 2019 Federal Reserve Payments Study estimates the total value of US card transactions for 2018.

Call it $7T in round numbers. If 5% of those payments are made via Apple Pay, then that’s $350B worth of transactions. If Apple takes 0.15% of that, then it made a cool $525M in 2018. If Bernstein is right that the percentage doubles to 10% by 2025, then that’s a billion-dollar business – from one country in one year.

We don’t have comparable Apple Pay usage estimates for other countries, and we’d need to look at total card transactions in each country and … well, that’s a student thesis right there. But employing the best advice I ever read on safely making predictions (‘give them a number or give them a date, never both’), it seems to me we can safely say that Apple Pay revenue is headed toward a multi-billion dollar business.

Not bad for free money.