How often does this need to be replaced?

Sponges should ideally be replaced every 3 months due to the potential for bacterial and mold overgrowth (is the professional answer) but I take good care of mine. I wash it before and after use and allow it to completely air dry in a spiral egg cup holder. How you dry it is very important. Since I don't use it every day anymore I think I've had this one for at least a year.