Hi, You're right - me too is more informal. So do I, so have I, so am I etc are more formal. To choose the verb, imagine the statement as a Yes/No question, and use the verb from the question. For example: I'm really tired => Are you really tired? (are is from the verb be, so the response is "So am I") I've been busy recently => Have you been busy recently? (So have I) Hope this helps Kathryn

You want to match the verb type. You: I am tired. Me: So am I. You: I like this movie. Me: So do I. Sometimes I can't think fast enough, and I will say "Me too" to express my agreement when the correct reply should be "Me neither."

So, we shouldn't use "so do I, .." when we talking about something negative?

HI there, it all depends on the context of your story. For example, I have a broken leg, or I'm tired its either what you are or what you have. the phrase me too can work generally for most if not all situations, however the same can't be said about the other two. Here I will demonstrate two bad examples. "Man! I'm tired", "so do I". "I broke my leg", " so am I".