We just got some hard numbers on the massive iPhone upgrade cycle that's coming

Apple sold 212 million iPhone in its fiscal year for 2016, down 8%. It's rare that the company fails to grow sales. The company has taken a beating as a result, and CEO Tim Cook now regularly comes in for harsh criticism.

"Steve Jobs's worst decision was promoting Tim Cook," a Quartz columnist wrote recently. "In five years the only truly new product that's managed to ship is the Apple Watch. And somehow, with 115,000 employees, Apple can barely get annual updates out for its laptops and desktop computers."

But hold that thought.

New data from Bernstein analyst Toni Sacconaghi Jr. and his team suggest that the next couple of years for Apple will make this period look like a blip. The "installed base" of iPhone users is now so massive, and the annual upgrade rate so consistent, that future iPhone sales will be driven by a self-generating "supercycle."

"Our analysis indicates that iPhone's installed base will be nearly ~80% larger entering the iPhone 8 cycle than it was entering the strong iPhone 6 cycle," he wrote in a recent note to clients.

The installed base of current iPhone users now stands at about 691 million phones, according to Sacconaghi. By 2018 that number is estimated to be 855 million:

By 2018, 203 million iPhones will become old enough that users are likely to buy a new model:

The upgrade rate stays at roughly 1 in every 4 iPhones in the installed base, annually:

In other words, Apple can expect to get a year's worth of new iPhone sales simply from the one-quarter of existing iPhone users who feel they will need a new phone.

So, Tim Cook may not have launched a new product as revolutionary as the iPhone, but he does deserve credit for creating a product so big that its future sales growth is a function of how massive its historic customer base is.