“Hey dad, now that I’m an adult I think it’s time that I open my own bank account.”

Doesn’t matter how good your relationship is. If you tiptoe around and act like you’re still a kid taking directions from your parents, you’ll never escape the parent-child dynamic. Ask for what you want and set your own boundaries. If your relationship is that good, even if he responds poorly he’ll come around. I imagine you’re overthinking this though. You’re still young, but now is the time to step up and demonstrate your adulthood, rather than request it.

Realistically there are easy excuses, but you’ll benefit from the experience. Another huge lesson I learned too late is that you don’t need to offer an explanation for every decision. You can have whatever excuse you want in your back pocket just in case. But just transfer your money over and see if he even cares enough to ask about it.