Facebook's WhatsApp messaging app keeps on growing. According to the company's CEO, it has more than 900 million monthly active users.

The app allows people all over the world to send text messages without facing carrier fees. In April, WhatsApp announced it had 800 million active users, CNET reports. In the past 12 moths, WhatsApp has grown its user base by 50 percent.

Facebook is realizing how popular WhatsApp is since acquiring the company back in 2014 for $19 billion. At the beginning of 2015, WhatsApp had 700 million users, compared to the 600 million it had in August of 2014. 

WhatsApp is not as popular as Facebook, which has 1.44 billion monthly active users, but it almost triples Twitter's active user base of 316 million each month.

"Congrats to Jan, the WhatsApp team and whole community on reaching 900 million people!" Facebook CEO Mark Zuckerberg said in follow-up post. 

Facebook may lead WhatsApp in total usage per month, but more people use WhatsApp to chat than they do Facebook's chat program Messenger. Facebook Messenger has 700 million monthly active users, as of a June announcement from the company.

WhatsApp started in 2009 as a rather basic text messaging app. Voice messages could also be left in the app and almost every mobile platform supports it. WhatsApp is now offering a brand new feature for voice calling, similar to Skype or other video chat apps.

Facebook wants WhatsApp to reach 1 billion monthly active users and thinks that money can be made once it reaches that number, USAToday reports.

"This may sound a little ridiculous to say, but for us, products don't really get that interesting to turn into businesses until they have about 1 billion people using them," Zuckerberg said in 2014.

Zuckerburg was excited when 1 billion people around the world used Facebook in one day and hopes that WhatsApp will be similar.

"This was the first time we reached this milestone, and it's just the beginning of connecting the whole world," Zuckerberg wrote.