Citi’s Mark May issued a new valuation estimate for the popular app, far above the bank’s prior $19 billion valuation, a loftier view on the asset that May attributed to Instagram’s announcement last week that it had reached more than 300 million total users.

“While Instagram is still early in monetizing its audience and data assets and its financial contribution to Facebook is minimal today, we believe that it is quickly gaining monetization traction and would contribute more than $2 billion in high-margin revenue at current user and engagement levels if fully monetized,” May wrote in a research report.

The sky-high valuation makes Facebook’s (FB) 2012 acquisition of Instagram look like a slam-dunk. The social-media giant only paid $1 billion for Instagram in a cash-and-stock deal.

And Facebook’s move to make money off Instagram is just getting started. Instagram began to roll out ads in its photo stream in late 2013, with video ads debuting on the platform roughly a year later. Citi’s May expects that 2015 will be the first year that Facebook begins to develop “more meaningful off-Facebook revenue streams,” and that includes efforts to make more money off Instagram.

Even with Instagram’s likely higher valuation, it is still a relatively small piece of Facebook, which is overall worth more than $220 billion. But the photo-sharing service’s new valuation estimate by Citi would suggest it is worth more than Twitter (TWTR), which has fewer monthly active users and a market capitalization of almost $24 billion.

That valuation gap could potentially widen. May said that he expects Instagram could continue to rapidly add users and expects the gap in total viewers between Instagram and Twitter will continue to widen. By the end of 2015, May forecasted that Instagram could have 420 million users verses Twitter’s 319 million.