How often do you replace your belt?

No, this is not one of those questions where I'm looking for an answer like, "After Thanksgiving." The belt on my table is over three years old. When I place the brush on the vinyl, it slows down now. I'm also questioning the sound quality lately, I'm thinking, the belt may need replacement. Does anyone have a formula? Like every year or so? In which case I'm long overdue? I just ordered a new Turbo power supply. Maybe all I needed to do was replace the belt? Hmmm...

Thanx,

Dave