The company crossed 700 million users in January.
Messaging service WhatsApp is on track to have one billion users later this year as the company hit the 800 million monthly active user mark recently.
WhatsApp co-founder and CEO Jan Koum made the announcement in a Facebook post: "WhatsApp — now serving 800,000,000 monthly active users. Reminder for the press out there: active and registered users are not the same thing."
In January, the mobile messaging service crossed 700 million users, sending over 30 billion messages a day.
Facebook acquired WhatsApp for about $22bn in October 2014. The app has reportedly added around 100 million users every four months since August.
Earlier this month, WhatsApp rolled out calling feature to all Android devices, and will be extended to iOS and Windows Phone users soon.
The new feature is expected to provide the company an edge over rival services such as Skype, FaceTime, Viber, and iMessage.
The company added end-to-end encryption into its service in November last year.