This is probably the most popular question! All medicare supplement (medigap) plans have a monthly premium. This is because the policies cover significantly more than the Medicare Advantage plan. Namely, medical bills! Many senior citizens switch from their Medicare Advantage plan to a supplement plan because it saves them a lot more out-of-pocket money in the end, especially if they have a pre-existing health condition or can develop one in the future. Paying a monthly premium can save you thousands in medical bills.