The market research firm eMarketer said in a report Thursday that nearly 35 million people in America accessed Instagram at least once each month as of the end of 2013, a jump of more than 30 percent from a year earlier.
And the report said nearly 25 percent of smartphone users in the United States will use Instagram at least once a month by the end of this year bringing the total user base to more than 40 million.
Twitter has around 43 million US users on computers and smartphones, according to eMarketer, which said the age of the microblogging service's users was broadening out while Instagram predominantly remains the preserve of younger users.
When looking at smartphone use with Instagram activity almost exclusively a mobile service Twitter's 30.8 million user base will increase to 37.3 million in 2014, the firm said.
"Overall, Twitter's US user base shows signs of maturing in its demographic composition, spreading the user population more evenly across age groups, while Instagram is still largely limited to a pool of millennial and Gen X users," eMarketer said.
Instagram in November began displaying ads as Facebook moved to start making money from the smartphone photo sharing service it bought in a billion-dollar deal in early 2012.