Instagram just blew through another important milestone

Instagram is closer than ever to a billion users.

The app now counts 800 million monthly active users, up from 700 million in April, the company announced Monday during a presentation at AdWeek in New York City. Of those, 500 million are users who return each day, Instagram said.

That stat stands in stark contrast to rival Snapchat, which had 173 million daily active users (DAUs) as of August. Snap hasn't announced how many monthly users Snapchat has.

More impressive than Instagram's sheer size, though, is how quickly it's still growing. The company said its latest growth was the fastest it's ever added 100 million new users.

The new growth is likely driven by a few factors, including the popularity of Instagram Stories. That feature alone has more than 250 million daily active users -- more than Snapchat's entire user base. Instagram has also made new efforts to reach new users in developing markets.

While those markets represent some of Instagram's biggest opportunities for growth, they've historically been challenging for the photo-sharing app. In the past year, though, the company has tested offline functionality and added mobile web sharing to appeal to users in developing markets.

Instagram's recent growth isn't just users; the company's advertisers has also grown. The service now counts more than two million advertisers, double what it had a year ago.