Rail systems around the world warn you to "mind the gap" when boarding a train. It's good advice for your Medicare coverage, too.
Medicare is comprehensive, but it doesn't cover everything. There are copays, deductibles, and limits on hospitalization benefits. If you enroll in Medicare Advantage--the all-in-one managed care alternative to traditional Medicare--your out-of-pocket costs are capped. But if you elect traditional Medicare, you'll probably want to buy a Medigap supplemental policy to close some or all of your gaps. Nearly 1 in 4 Medicare enrollees have a Medigap policy, according to the Kaiser Family Foundation.