When you sign up for Medicare, it’s logical to focus on your premiums while making coverage decisions.

However, two other factors actually are more important: your access to care and the risk of high out-of-pocket costs.

And if you enroll in traditional Medicare, getting that out-of-pocket protection probably boils down to just one word: Medigap.

Traditional Medicare offers much more flexibility in how you access medical care when compared with Medicare Advantage plans, which typically use managed-care provider networks. However, Advantage plans come with a built-in cap on out-of-pocket costs–a feature that traditional Medicare lacks. Some traditional Medicare enrollees receive supplemental gap insurance as a retirement benefit from their former employers to cover some of those out-of-pocket costs.

Lower-income seniors may receive help from Medicaid. But for everyone else, it’s essential to understand the ins and outs of Medigap–when to buy it, the plan options, and how to go about selecting a plan.