SO DO I vs. ME TOO

English learners are often confused about

when to use “SO DO I” and when to use “ME TOO”. Do you know the difference between SO DO I and ME TOO, and when to use them? Read on!
SO DO I vs. ME TOO
Both SO DO I and ME TOO are used as a response to simple statements. The statements must be positive (without the word “no” or “not”).  SO DO I is more formal, while ME TOO is more informal.

ME TOO
ME TOO is more informal. It is used in casual conversation.
>I love ice cream. Me too.
>I slept so well last night. Me too.
 
What about negative sentences? For these, we say ME NEITHER.
>I can’t dance. Me neither.
>I didn’t sleep well last night. Me neither.
 
SO DO I
SO DO I is more formal. It is used in writing, in more formal conversations, and in presentations.
>I love the book The Sun Also Rises. So do I.
>I think she did an excellent job on her presentation. So do I.
 
SO + [WORD] + I
Note that we can use SO + [WORD] + I/SUBJECT with other positive statements. The middle word must match the verb or verbs of the first statement.  
Use DID if the original positive statement is in the simple past.
>I loved the book Charlotte’s Web when I was a child. So did I.
 
Negative statements
What about negative statements? We can’t use SO DO I or its variations. We must use NEITHER. Use the form NEITHER + [VERB/MODAL] + SUBJECT. Make sure that the verb or modal from the original statement matches the verb/modal in the “neither” statement.
>I can’t dance. Neither can I.
>I’m not ordering dessert. Neither am I.