When Windows 10 launched, Microsoft claimed it would have the new operating system on a billion devices by mid-2018. That isn't going to happen, however, Redmond has now admitted.

For the past year, Microsoft has offered the new OS as a free upgrade for both desktop and mobile users (provided the phone can handle it in the latter case), and has been pushing it for Internet of Things makers. However, so far the OS is only on 350 million monthly active devices, and Redmond says it needs more time to hit ten figures.

"We're pleased with our progress to date, but due to the focusing of our phone hardware business, it will take longer than FY18 [the year to July 2018] for us to reach our goal of one billion monthly active devices," a spokeswoman told The Reg.

"In the year ahead, we are excited about usage growth coming from commercial deployments and new devices – and increasing customer delight with Windows."

The admission shows that the persistent nagware on PCs for users of Windows 7 and 8.1 hasn't worked, despite Microsoft attempting some fairly underhanded tactics to get people to upgrade, and may have soured some on the OS.

Enterprises, which were thought to be big believers in the new operating system, have also been unimpressed. Sure, there are pilot programs running in many companies, but IT managers have shown little willingness to do a mass upgrade when earlier operating systems are still working well.

The other failure point is with Microsoft's mobile strategy, or lack of one these days. Windows Phone sales are cratering, it's not a popular OS with vendors, and although Microsoft says it is still developing the platform, their OS is short on apps and customers.

Microsoft can expect an upsurge in Windows 10 installations from PC users toward the end of the month, when the free upgrade offer ends. But with PC sales disappointing, mobile users a dying breed, and enterprise not biting yet, it's clear Microsoft will need longer than two years to hit the billion mark. 2020 perhaps? ®