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Office 365 is one of Microsoft’s top sources of revenue. “We also see momentum amongst consumers, with now more than 23 million Office 365 subscribers,” Microsoft CEO Satya Nadella said. However, analysis of Office 365 numbers may indicate that its “momentum” has actually slowed down.

Per Computer World, the 23.1 million subscriber count cited by Microsoft in its filing with the U.S. Securities and Exchange Commission (SEC) for the June quarter, represents a 52-percent increase over the same period last year.

However, despite the rather big number, year over year growth of Office 365 subscription is on a continuous decline since several years. A year before, the June 2015 quarter sported a consumer Office 365 subscription growth rate of 171% over the same three-month span in 2014.

Microsoft did not address the issue directly. However, it did see a similar trend of maintaining percentage increases on its corporate subscribers.

The company explained it will be hard to top off the raw number of subscriptions their services have.

“We’re getting a very big base,” chief financial officer Amy Hood said. “And so while we feel great about continuing to add seats at that type of rate, converting and adding net new into our install base, you will see that growth rate come down just because the business is getting quite big.”