(a decision) is up to (someone)

You can say that a decision "is up to" a certain person. This means that this person gets to make the decision. For example:

A: What do you want for breakfast?

B: It's up to you.

When you say "it's not up to me", it means that you don't have the authority to male a decision; someone else has to decide.

This phrase appears in these lessons: