When to replace a bike helmet

The rule

Replace a bike helmet after any crash or hard impact, even if it looks fine. The foam liner is built to crush once and absorb that energy; after it has done its job, it cannot do it again. The US Consumer Product Safety Commission says to replace a single-impact helmet after a crash "even if there are no visible signs of damage", and the CDC's HEADS UP programme says the same for any helmet that is damaged or has been in a crash.

Without a crash, replace it with age. The Snell Memorial Foundation recommends replacement about every 5 years. The CPSC says "it may be prudent to replace your helmet within 5–10 years of purchase". This calculator uses 5 years as its starting point and shortens it for heavy use and hot storage. There is no kilometre rule for helmets: time, sweat, sunlight and knocks matter more than distance. This check is one of the free LeCoach cycling calculators.

The signs: how to check

Take the helmet off your head, remove the pads and look at it in good light. It takes two minutes.

• Production date sticker. Look inside the shell for a label with the production date. Count from that date, not the day you bought it, because a helmet can sit in a shop for a while.
• Cracks or dents in shell or foam. Check the outer shell and the foam underneath, especially at the edges. Any crack or dent is a hard sign: replace it.
• Compressed or crumbly foam. Press the foam with your thumb. If it is flattened in one spot or flakes, replace it. Also a hard sign.
• Broken buckle or frayed straps. A helmet that can come off in a crash cannot protect you.
• Loose or damaged MIPS layer. If your helmet has a low-friction liner, it should move slightly and sit securely in its clips.
• Fit is loose even when tightened. Worn retention systems and pads can leave the helmet rocking on your head.

Estimate yours

The calculator works in years, not kilometres.

• Helmet age (years since production date). Read it off the sticker inside.
• Crashed or hit my head in it. If this is on, the answer is always replace, whatever the age.
• Dropped it hard on a hard floor. Moves the verdict to "Check it soon" so you inspect it properly.
• Stored in a hot car or attic. Heat can affect the foam and shell, so the calculator takes a year off the 5-year limit.
• Days a week I ride. At 5 or more days a week, sweat, sunlight and handling add up, and the calculator takes another year off.

Within a year of your limit, the verdict becomes "Check it soon". At or past it, "Replace it".

Common mistakes

• Keeping a helmet after a crash because it looks fine. Foam can be crushed without visible damage. Helmets are built to absorb one impact.
• Counting from the purchase date. Use the production date on the sticker.
• Buying second-hand. You cannot know whether it has been crashed.
• Leaving it in the car. A parked car in summer can get very hot.
• Wearing it too loose or tilted back. The helmet should sit level, about two finger widths above your eyebrows, with straps snug under your ears and chin.
• Painting or putting stickers on it. Some paints and solvents can weaken the shell or foam. Check the maker's instructions.

When the estimate changes

• Daily commuting or training 5 or more days a week shortens helmet life.
• Hot climates and hot storage age the materials faster.
• Any crash, drop or knock resets the question. Inspect it straight away.
• Fit changes, for example with a new haircut or a winter cap underneath, can make a sound helmet sit poorly. Adjust it, and see what to wear cycling for cold-weather layers that fit underneath.
• Before a big event, check the helmet as part of your race day checklist.

For the rest of your kit, use the bike maintenance schedule and check when to replace bike tires. LeCoach coaches the training; you bring the helmet. Ask the coach anything about your riding.