The global app economy is expected to more than quadruple in size within the next four years.

That's according to a report released this week from research firm App Annie, which estimates the current $1.3 trillion market could grow to a whopping $6.3 trillion by 2021.

That value encompasses advertising, in-app transactions, and other forms of mobile commerce as well as sales of the apps themselves.

SEE ALSO:The mobile online shopping revolution is definitely coming—but nobody's sure when

Meanwhile, the number of app users worldwide will double to 6.3 billion, researchers predict, suggesting that business opportunities to squeeze maximum cash from each app user are far from fully realized.

Indeed, App Annie estimates that the average mobile user currently spends around $379 on apps each year—a figure that includes the monetary worth of attention paid to ads. By 2021, that amount is expected to swell to $1,008.

Maybe that's because the total time we spend in mobile apps is expected to pass 3.5 trillionhours by that year.

The biggest driver of this growth will come in the form of an explosion in mobile online shopping and other in-app commerce. While the category is growing fast and industry experts have talked of a smartphone commerce revolution for years, people still tend to do the vast majority of their shopping on desktop.

But that reality is changing fast as companies find new ways to make navigating small screens easier and assure customers that their money is safe on their phone.

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"Clearly, commerce is the dominant portion of these numbers. As mobile payments become more widely integrated in apps and adopted by consumers, retail, ride hailing, grocery, travel, and many more, industries will drive (or get left out) of this transition," said Danielle Levitas, senior vice president of Research and Professional Services at App Annie. 

Credit: app annie

Advertising will also be a major driver as ad tech companies find more efficient and less annoying ad formats and more precise ways of tracking and targeting ads.

Beyond that, growth will be further fueled as the mobile revolution begins to hit perviously untapped new industries.

"We haven’t even started to see the impact of mobile and apps in other areas, like health, so there is even more upside long term," Levitas said.    

The growth is expected to be slanted towards developing markets where it's often easier to roll out mobile technologies on a large scale because there isn't as much established infrastructure to stand in their way. That's consistent with trends in mobile payments, commerce, and social media, among other things.

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App Annie uses an algorithm to forecast the app marketplace, pulling data from more than 30,000  economic, demographic, behavioral, and technology sector-specific sources, including the U.S Census Bureau and the European Central Bank.

As for how we're spending our time, App Annie highlighted gains in a few categories. Travel app usage went up as much as 75 percent in many countries. Gaming, long one of the most dominant categories, also saw gains — particularly in Japan and South Korea where "hardcore mobile gamers" (defined as the top 10 percent of most active gamers by App Annie) are spending nearly three hours a day playing games. 

Other notable stats: The U.S. was the leader in app creation in 2016, with new Google Play and iOS apps making up 24 percent of the total app releases. China came in second with 15 percent of the world's new apps, followed by 9 percent from Japan, 7 percent from Germany, and 6 percent coming out of South Korea. 

Here's to a future of even more time and money spent on apps. 

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TopicsApps & Software