Have you ever wondered how much you spend on iPhone apps? It might be more than you expected.

The average iPhone owner in the U.S. spent $35 on apps last year, according to Sensor Tower, an app-marketing company. The total amount includes both downloads of paid applications, as well as in-app purchases.

Not surprisingly, given how popular gaming has become on mobile devices, that’s where most of your cash is going. According to Sensor Tower, which based its data on 110 million active iPhones in the U.S., the average American spent $25 on games last year, a whopping 635% more than the $3.40 they spent on music-related app purchases. Social networking, entertainment, and “lifestyle” apps rounded out the top five, with users spending an average of $1.80, $1, and 40 cents on those app types, respectively.

Apple’s AAPL App Store has become an increasingly popular destination for users to extend the usability of their iPhones and iPads. In January, for instance, Apple announced that it registered a “record-breaking holiday season for the App Store” in 2015, with customers spending $1.1 billion worldwide on apps and in-app purchases during the two-week period ended Jan. 3.

Get Data Sheet, Fortune’s technology newsletter.

Apple was quick to note that gaming, social networking, and entertainment apps—the same categories that delivered the most revenue to developers in the Sensor Tower study—were most popular during that period.

Apple said in January that it has paid out nearly $40 billion to developers since the App Store’s inception in 2008. The company added that over one-third of that developer revenue was generated in 2015, alone.

It’s worth noting that Apple also benefits from the App Store’s popularity. Before it pays out that cash to developers, the company takes a 30% cut of the revenue generated off paid downloads and in-app purchases.

Still, the market is changing. As several studies over the last couple of years have shown, consumers across Apple’s iOS, as well as Google’s Android, are increasingly choosing so-called “freemium” apps, or programs they can download for free, but include in-app purchases or ads that help developers generate revenue off their creations. While that has hurt the paid-apps market, a study last year from IDC and App Annie found that mobile app revenue was actually up, despite changing consumer desire.

For Tim Cook’s take on Apple’s iPhone apps, watch:

In addition to analyzing how much iPhone owners spend on their apps, Sensor Tower also examined 2015 U.S. App Store downloads. The company found that the average iPhone owner last year downloaded about 10 games and more than three “photo and video” apps. Those same users downloaded more than three social networking apps and nearly three entertainment programs.

“Of the remaining 18 categories with downloads during the period, Music saw the most with 2.2 installs on average, while Catalogs saw the least with 0.17 per device,” Sensor Tower said in a statement.

So, what can app developers learn? According to Sensor Tower, Americans are most willing to spend money on games, suggesting that a solid title could help generate some revenue. The company also provided some insight into how to make some cash on iPhone users, even if an app isn’t so popular.

These are the most popular iPhone and iPad apps ever

“It’s much more difficult for Medical apps to secure installs, by comparison, as they are the second least likely to be downloaded after Catalogs at an average of 0.2 per device in 2015,” the company says. “These apps have the third-highest average gross revenue per install at $0.57, however, which may make the acquisition of these users worth the effort.”

Regardless, at least now you know what you’re spending on your iPhone apps.