I always dress for an interview one step above the "norm" as a nod to the formality of the occasion. So if everyone dresses in jeans and a t-shirt I might wear

I always dress for an interview one step above the "norm" as a nod to the formality of the occasion. So if everyone dresses in jeans and a t-shirt I might wear slacks and a polo or jeans and a button down shirt. If they wear business casual I'd probably wear a suit (though probably sans jacket).