In an investor note obtained by CNBC, Sacconaghi says that people are waiting longer than ever to upgrade which could spell trouble for Apple.
"Replacement cycles are elongating ... a lot," Sacconaghi said, noting that people are using their iPhones longer because of Apple's battery replacement program, changes in carrier subsidies and higher prices, among other reasons.
Apple CEO Tim Cook confirmed this himself on a recent earnings call. "Our customers are holding on to their older iPhones a bit longer than in the past," said Cook.
It's estimated that 16% of Apple's installed base will buy a new iPhone in 2019 and Sacconaghi doesn't believe that the company's fiscal 2020 offering will stimulate an acceleration in iPhone replacement cycles.
The analyst predicts that despite the iPhone's install base growing 9% last year, units will be down 19% in fiscal 2019. However, Sacconaghi cautions that there is a "myriad of unknowns" and notes that "modeling iPhone's installed base is as much art as science".
While Apple stopped revealing unit sales for iPhone, it reported an install base of 900 million iPhone devices in use right now.
More details in the full report linked below...