How long is my helmet good for?

If foggy memory serves me right, Snell foundation up dates their standards every 5 years, so ( for arguments sake ) if your helmet is Snell 2015 standard, next up date is 2020, so ( again foggy memory ) rule book states that helmet must be current or previous standard; 2025 standard will render your 2015 standard helmet unusable.

Does this help?