WhatsApp had 450 million monthly active users when Facebook announced its acquisition in February 2014.
Facebook’s February 19, 2014 announcement described WhatsApp as having over 450 million people using the service each month. It also said that 70% of those users were active on a given day, showing that WhatsApp’s audience was not merely registered but highly engaged.
The acquisition valued WhatsApp at approximately $19 billion when restricted stock units for employees and founders were included. Facebook’s initial announcement described about $16 billion in cash and shares, plus an additional $3 billion in restricted stock.
The number is often confused with nearby milestones. WhatsApp had 400 million monthly active users in December 2013, then exceeded 500 million by April 2014. Thus, 450 million is the canonical quiz answer for the acquisition announcement, even though contemporary sources often phrased it as “over 450 million.”