Ever since day one, Twitter always counted everything within the text box in its 140 character limit. This meant that if you were replying to someone their user names would eat up part of your 140 characters. Similarly, if you included a URL or uploaded a picture, the link will also take up part of the 140 characters.
This is going to change in the coming months. Twitter has announced four changes that should let you get the most out of the 140 characters.
First, usernames within a reply tweet won't count towards the characters. This means even if you're replying to one or multiple people, you don't have to worry about running out of characters for your tweet.
Second, links in tweets also won't count. Where it is image or video link, polls or quoted tweets.
Third, you can now retweet yourself, if that's something you want to do.
And lastly, you don't need to add a period before @ so you can tag someone and also have the tweet seen by your followers. You will be able to start a tweet with someone's username and as long as it's not a reply, it will be visible to your followers. And if you want your followers to see a reply, you will be able to retweet it, as mentioned before.
Twitter will be rolling out these changes over the coming months so developers have the time to incorporate them within their app.