It is up to you

John : Would you like to go out to dinner or to a movie ?
Karen : Either one, it is up to you .
John: What would you prefer ?
Karen: I really don't care, I just want to get out of the house.
John: Well, then how about dinner and a movie ?
Karen: That's a great idea !

Explanation :
If you say that it is up to someone to do something, you mean that it is their responsibility to do it.

Example : -
The choice was up to Paula.