In just two months since Facebook dropped $19 billion to buy WhatsApp, the five-year-old mobile messaging app on Tuesday announced its active user base has grown to more than half a billion people.

On February 17, the day it was acquired by Facebook, the company said it had 450 million monthly active users worldwide and over 320 million daily active users.

“In the last few months, we’ve grown fastest in countries like Brazil, India, Mexico, and Russia, and our users are sharing more than 700 million photos and 100 million videos every single day,” WhatsApp said on its blog. “We could go on, but for now, it’s more important that we get back to work.”

Facebook: The Key To Growth

This is not the first time that an app has seen a major pop in users after it was acquired by Facebook. When Facebook bought Instagram in April 2012, the service boasted some 30 million users. In one month after the deal, Instagram gained 20 million new users. By July, Instagram grew to 80 million active users. Adding an Android app in addition to its iPhone app certainly helped, but the Facebook effect is a definite reality. Instagram managed to increase its user base by more than 10 million users on average per month.

WhatsApp seems to be having a similar growth spurt, gaining roughly 25 million users each month since the Facebook deal was announced. Even for an app with astronomic growth like WhatsApp, those are impressive numbers.

It’s clear that WhatsApp has the legs to grow in both developed and emerging markets, especially as a cheap alternative to SMS. The chart below from analytics firm comScore (which doesn’t include WhatsApp’s fifth year of existence) shows just how much the service had grown prior to being bought by Facebook.

At this rate, it should only take less than a year for WhatsApp to reach a billion users worldwide.

Facebook is still in the process of completing its $19 billion purchase of WhatsApp, which included cash and various stock options. The deal has been approved by the Federal Trade Commission but still needs international regulatory approval before the purchase can become final.