Asymco analyst Horace Dediu this week shared new research that determines lifespan of a typical Apple devices. The proposal is based on last month's earnings call, when Tim Cook says that there are 1.3 billion of active Apple devices, so if you use the number of active devices and cumulative devices sold, you can get to the average lifespan.
As can be seen from the figure above, Dediu found that the cumulative total sales of Apple devices reached 750 million units in the second quarter of 2013, so by default, 750 million devices sold before 2Q of 2013 were officially eliminated in the fourth quarter of 2017, as the products released after 2013 are still in use, which is how he got the idea that average lifespan is little four years.
Here’s how to compute this yourself: Visually, the lifespan is the distance horizontally between the two vertical bars such that the bars are the same length. The top vertical bar measures the gap between the area (cumulative devices) and the curve (active devices) and the lower bar is the gap between the area and the x-axis, i.e. the cumulative devices. When those two bars are the same size the distance between them is the lifespan (at the time of the top bar.)
Arithmetically, the average lifespan at a given time t is the duration between t and the moment when the cumulative devices sold reached the cumulative retired devices at time t.
For example today–as the visual above represents–the lifespan is the time since cumulative devices sold reached the current total retired devices. The cumulative retired devices can be calculated as 2.05 billion cumulative sold minus 1.3 billion active or 750 million. The time when cumulative devices sold reached 750 million was the third quarter 2013. The lifespan is thus estimated at the time between now and Q3 2013 or 17 quarters or about 4 years and three months.
Interestingly, the analyst provided another picture that showed us how average lifespan of Apple device has changes from time to time. It appears that the lifespan has dropped from 8 quarters to 4 quarters before and after 2011, that's because when iPhone 4/4S released, it promoted users to switch to new iPhone at that time. Following super cycle, the lifespan has gotten all the way up until now days of 17 quarters.