BHSI and Snell both say five years. That's a recommendation that's been in place since long before the current lightweight helmets. So, three years vs. five might be marketing, or it might be based on the fact that newer helmets have so much more surface area and places to degrade, and so much less protective material. But five years is what the safety organizations say and that would be my outer limit. Isn't the possibility of avoiding traumatic brain injury worth $40 or $60 to you? Or even $300 if you want a top of the line helmet?