News of the milestone came in a tweet, of course, from the official Twitter account: "There are now more than 200M monthly active @twitter users. You are the pulse of the planet. We're grateful for your ongoing support!"
The number was the first official estimate from Twitter since it claimed 140 million active users.
Twitter offered no details on the latest update, but in the past has said the majority of active users were in the United States.
Outside analysts have provided various estimates for Twitter, which is privately held and thus not required to disclose most business data.
Earlier this year, a French-based research firm said over 500 million people are on the micro-blogging site, with Americans and Brazilians the most connected.
Another group, Sys-Con media, estimated last month that Twitter had over 465 million accounts and that the number of daily tweets had topped 175 million.
A recent survey found one in seven Americans who go online use Twitter and eight percent do so every day.