Instagram announced this week that it has surpassed 200 million monthly active users.

eMarketer is now sharing some data about usage in the U.S. and a comparison to Twitter usage on smartphones. The firm finds that U.S. Instagram usage has already nearly reached the same level as U.S. Twitter usage on smartphones among millennials and Gen Xers.

Based on eMarketer’s estimates, about 35 million people in the U.S. accessed Instagram at least once a month last year, and this year 25% of U.S. smartphone users will do so.

“User counts for Instagram and Twitter are strikingly similar,” eMarketer says in its report. “eMarketer estimates that 43.2 million US consumers used Twitter monthly last year—or 17.6% of the total internet user population. Meanwhile, Instagram users represented 16.1% internet users. Limiting that figure to smartphone Twitter users, Twitter hit just 30.8 million in 2013; this will increase to 37.3 million in 2014, or 22.7% of US smartphone users. Both figures fall slightly below those for total Instagram users, and while Instagram activity all but exclusively takes place on smartphones (meaning Instagram’s smartphone user base could be higher than Twitter’s), it is possible for Instagram users to have an account online without accessing the service through a smartphone. As a point of reference, eMarketer pegs US smartphone Facebook users at 123.7 million this year.”

It took just over a year for Instagram to double its monthly active user count from 100 million. The company says it has exceeded 20 billion photos shared to date.

Twitter said last month that average monthly active users were 241 million by the end of last year, up 30% year-over-year. Mobile monthly active users were 184 million in Q4, up 37% year-over-year, representing 76% of total MAUs.

Image via eMarketer