Bob's given you the correct answer...... and I'll add advice to wear one even if you don't have to.
Helmets are cheap, effective protection against injuries you can't recover from. Its easier than you think to bash your head in on a bike, even just riding around your own neighborhood. If you live long enough to go over 100,000 miles as I have, you'll figure that out for yourself.
Regardless of how good a rider you are, stuff happens. A suddenly flat front tire in a turn is taking you down. If you're near the curb, there goes the noggin. Been there done that (with a helmet fortunately).
Ride safe, wear the helmet.