grammaticality - "For how many days have you been there?"

I read the following and was wondering if it was grammatically correct? Can we use this if the person just moved from that place and you run into him in a new place?

For how many days have you been there?

http://m.fanfiction.net/s/2086227/16/

Answer

If the person is still in the place referred to as there, then the question How many days have you been there? (present perfect) is the only grammatically correct choice.

If the person is no longer there, then the question must be How many days were you there? (past simple).

Note: how many is sufficient; it doesn't need to be for how many.