This guide is for general information only and is not legal advice. Laws change — verify current rules with your state DOT or a licensed attorney before relying on this for any legal matter. Read full disclaimer.
Massachusetts requires a bicycle helmet for any rider under the age of 17. The same rule extends to children carried as passengers in a child seat or trailer. Non-criminal violation; no fine in practice for first offense. The statute applies to anyone aged 16 or younger and to passengers carried in a child seat or trailer (passengers must be at least one year old). See Mass. Gen. Laws ch. 85, § 11B½.
If you're 17 or older, Massachusetts doesn't require you to wear a helmet by state law. Riders under 17 (and any child carried as a passenger) must wear a helmet that meets the ANSI Z90.4, Snell, or ASTM F1447 (CPSC-certified helmets meet these specifications) standard.
Cities can be stricter than the state floor, and bike-share systems often require helmets regardless of age. If you're renting or commuting in a major city, confirm the local rule before you ride.