What should my explanation for taking a year and a half off be to people I meet at my new college after taking time off for depression?

I'm transferring colleges, I should be a junior but I'm only a freshman because I took a year and a half off. When I say I transferred and people ask what year I am what should I say? What should I say as to why I took a year and a half off? I did it because I had depression. But what should I say when people ask what year I am/ why I transferred