Medigap plans supplement your Original Medicare benefits, which is why these policies are also called Medicare Supplement plans. You’ll need to be enrolled in Original Medicare to be eligible for Medigap coverage, and you’ll need to stay enrolled in Original Medicare for your hospital and medical coverage. Medicare Supplement plans aren’t meant to provide stand-alone benefits.

Depending on the state that you live in, you may not be able to get Medicare Supplement coverage if you’re under 65 and have Medicare because of disability, end-stage renal disease, or amyotrophic lateral sclerosis. States aren’t required to offer Medigap coverage to beneficiaries under 65. If you’re under 65 and enrolled in Original Medicare, check with your state’s insurance department to find out if you’re eligible to enroll in a Medicare Supplement plan.

Keep in mind that Medigap plans don’t include prescription drug coverage (Part D), so if you want help with your medication costs, you’ll need to enroll in a stand-alone Medicare Prescription Drug Plan. In addition, you can’t use your Medicare Supplement plan to pay for costs you may have with a Medicare Advantage plan. Medigap insurance can only be used to cover costs in Original Medicare.

If you have Original Medicare and a Medicare Supplement plan, Original Medicare will pay first, and your Medigap policy will fill in the cost gaps. For example, suppose you have a $5,000 ambulance bill, and you have already met the yearly Medicare Part B deductible. Medicare Part B will pay 80% of your ambulance bill. If you have a Medicare Supplement plan that covers Part B copayments and coinsurance costs, then your Medigap policy would then pay the remaining 20% coinsurance of your $5,000 ambulance bill. Some Medicare Supplement plans may also cover the Part B deductible.