It's up to you
If you say to someone "it's up to you"; you are telling them that they are the one to make the choice, that it is their decision or it depends on them
A: Do you think I should take the job?
B: That's up to you. You'd earn more but remember that you'd have a longer journey to work.
A: I can't make up my mind. Should I buy the red or black one?
B: It's up to you. You look great in both.