What's it to you?

What's it to (one)?

What does one care? What business is it of one's? I pay my rent and my share of the bills—what's it to him how I spend my money otherwise? What's it to them what I do on the weekends? That's my time to do as I like! A: "Do you mind if I do yoga in the living room?" B: "Of course not! What's it to me?"

What's it to you?

Inf. Why does it matter to you?; It's none of your business. (A bit contentious.) Tom: Where are you going? Jane: What's it to you? Mary: Bill's pants don't match his shirt. Jane: Does it matter? What's it to you?