An analyst estimated how long Apple customers hold onto their devices — and the findings might surprise you (AAPL)

During its last earnings call, Apple announced that there are 1.3 billion active devices in the world.
Given that a little over 2 billion Apple products have been sold, we can calculate how many inactive devices are around.
Asymco analyst Horace Dediu used this number to figure out the average lifetime of Apple devices.

The quality of a product can be measured by how much time users hold on to it, and it looks like Apple customers are, on average, getting happier over time.

In a new research article published by Asymco analyst Horace Dediu, who follows the Cupertino giant closely, we now have a peek at the average lifetime of an Apple device (be it an iPhone, iPad, Apple Watch, or Mac), which has now reportedly surpassed four years.

How did Asymco calculate this, you ask? It's simple: It used the data Apple gave them.

During the latest earnings call, the iPhone maker has disclosed two key metrics, one of which is usually kept under wrap, i.e. the number of currently active devices: 1.3 billion (a 30% increase over 2016, when Apple announced the 1 billion figure).

Apple has so far sold some 2.05 billion devices, so if you take out the 1.3 billion computers, phones, and tablets now in use you remain with 750 million Apple products no longer in use.

Given that Apple's cumulative device sales reached 750 million in the third quarter of 2013, "The lifespan is thus estimated at 17 quarters or about 4 years and three months," Dediu wrote.

The correlation is clear in the graph above; if you consider any point in time on the X-axis where you know how many devices are active over the cumulative number of devices sold, you can take their difference (750 million devices as of now) and trace back the moment when that was the cumulative number of devices sold.

The time difference between the two quarters is the (average) lifespan.

This is important for understanding two things: One is that consumers upgrade to a new device less frequently than the market cycles refresh, and secondly that Apple customers seemingly are increasingly more satisfied with their purchases, and keep their computer or mobile device for longer.

Beyond overall sales and the number of active products, we now have a third insight on "the specific length of time or duration of use per device," Dediu said, "a proxy for user satisfaction and loyalty."

"[And] this is the most important measure of the health of a business, because it speaks of the future and not, as all other figures do, the past."