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.
Delaware requires a bicycle helmet for every rider under 18 — in practice, every rider except adults aged 18 and over. The same rule extends to children carried as passengers in a child seat or trailer. Civil violation; fine of up to $25 for a first offense. The court must waive the fine on proof that the rider has obtained a CPSC-certified helmet within 30 days. See 21 Del. Code § 4198K (Bicycle helmets required for persons under 18).
If you're 18 or older, Delaware doesn't require you to wear a helmet by state law. Riders under 18 (and any child carried as a passenger) must wear a helmet that meets the CPSC (16 C.F.R. Part 1203). 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.