The English idiom it’s up to you means:

• it’s your decision
• it’s your choice
• you can decide

We use it when we want to let another person take a decision, without us getting involved in the decision-making process.

It may be that we can’t decide ourselves, or we don’t have an opinion. It may be that the decision is particularly difficult and we don’t want to get involved – and get the blame if it goes pear-shaped (goes wrong)!

You want the full responsibility for the decision – and all of its consequences – to lie with the person whom it will most affect. Maybe because your help could backfire: if you make the wrong decision for your friend it could negatively affect your friendship:

Alex: I’m thinking about applying to Exeter University.

Sue: OK.

Alex: But I can’t decide. I really like Edinburgh.

Sue: I don’t know.

Alex: But what do you think? They’re both great universities. Come on. You must have an opinion.

Sue: It’s up to you, Alan. I really don’t want to tell you what to do.