In its first quarter 2015 earnings announcement today, Facebook revealed that it now has more than 1.44 billion monthly active users (up 13 percent year-over-year). Of those, 1.25 billion were mobile users, an increase of 24 percent year over year.

Facebook also shared that it now has 936 million daily active users (a 17 percent bump year over year) and 798 million mobile daily active users (a 31 percent increase year over year). This means about 65 percent of Facebook’s members use the service daily, and 64 percent of its mobile members use it daily on mobile.

While it’s great for Facebook that all these numbers are still growing, albeit slowly on a quarter-over-quarter basis, the real interesting figure is in the company’s earnings slides, on page 7:

fb_q1_2015_mobile_only

Between the fourth quarter 2014 and first quarter 2015, Facebook added 55 million mobile-only users to reach 581 million total (up 10.5 percent quarter-over-quarter). Mobile-only users now account for 40.34 percent of the social network’s total members. This number climbs every quarter, and it will likely reach the 50 percent mark at some point next year.

Here is how Facebook distinguishes this category:

Mobile-only MAUs are defined as users who accessed Facebook solely through mobile apps or mobile versions of our website, or used our Messenger app, in the last 30 days of the given quarter. The number of mobile-only MAUs do not include Instagram users unless they would otherwise qualify as such users based on their other activities on Facebook.

In other words, this is the number to watch. While Facebook’s growth continues to slow due to its size, its revenue share coming from mobile continues to grow. Mobile-only users are key to a social network that has managed to successfully transform itself into a mobile-first business.

Here are the other four charts for the numbers Facebook traditionally highlights in its releases:

fb_q1_2015_monthly

fb_q1_2015_mobile

fb_q1_2015_daily

fb_q1_2015_mobile_daily

Facebook will likely soon start underlining mobile-only numbers directly right in its press releases. It will be the fifth metric the company shares, on a quarterly basis, but the most important one.

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