Apple models new iPhones replaced after 3 years

Apple says it expects people to use a new iPhone and Apple Watch for just three years before replacing it, while a Mac is expected to stay with its first owner for four years.

In its latest environmental push, Apple released a document about how it calculates how much its products contribute to the greenhouse gas lifecycle. One of the metrics it detailed was "years of use".

"Years of use, which are based on first owners, are assumed to be four years for OS X and tvOS devices and three years for iOS and watchOS devices," the Cupertino, CA-based firm said.

Of course, this is just what Apple thinks people are doing based on its own data. And given the fact the Watch has only been out for a year, it's a forecast on Apple's part.

Analysis earlier this year from IHS showed that of the iPhone models in active use, 29 percent are iPhone 5 models and 23 percent are even older iPhone models. The iPhone 5 was launched in September 2012, which was over 3 years ago.

Apple's software updates had not always supported older iPhone models however. But from iOS 8, released in 2014, this changed. iOS 8 and the latest iOS 9 both support the iPhone 4s, which came out in October 2011.

Macs, of course, like many computers have a typically longer refresh cycle.

While Apple is not saying that it expects it devices to break down, the comments show its thinking when it comes to product cycles.

In the same document, other eagle-eyed observers noticed a slip-up by Apple in the way it refers to its operating system (OS) for its Macs. While the statement refers to "OS X" – the name of Apple's OS on Macs and Macbook's – the original statement referred to "MacOS" until it was quickly changed.

It's unknown if this was a genuine mistake or it could indicate a rebranding of the operating system.

CLARIFICATION: An earlier version of this article was unclear about what metric Apple was calculating for its devices.