Since I rarely crash I can't use that as a time frame, so I replace it when either the padding wears out or the styrofoam starts to degrade leaving tiny pieces of it on my forehead after a ride. Padding today is not as durable as it once was, so I'm finding my padding now wearing out before the styrofoam degrades, it use to be the other way around. The older helmets the styrofoam would start to degrade between 5 to 6 years, now the padding is shot in 2 to 3 years; I'm sure that is a purposeful thing.