be up to

(from Idioms in Speech)

dependent upon, depending upon the decision of

I suspected that it ought to be up to me whether we fought or not. (I. Murdoch)

They accepted him without much curiosity and with complete friendliness. He was Rosa's business, and it was up to her to make something of him. (J. Wain)

It wouldn't be necessary if we'd heard more of the truth perhaps when there was an inquest. And it's up to you, Olwen. You were the last to see Martin. (J. Priestley)

Erik felt only a frustrated realization that no matter how he worked, from this point on, his future was squarely up to Haviland. (M. Wilson)

It was up to him to put the kite right. (W. S. Maugham)

I'm not concerned with that. It's up to you to find out who'll lend the money to you. (J. Wain)

"You find out, I think, whether the job you hired him to do was humanly possible." - "That's up to the man who takes the job." (J. Galsworthy)