Medicare Part B or a Medicare Advantage plan should cover 100% of yearly screening mammogram costs and 80 percent of necessary diagnostic mammogram costs. As a Medicare beneficiary, you will pay nothing for yearly mammograms. If your doctor determines it to be medically necessary, Medicare will also cover diagnostic mammograms more frequently than once a year. Generally, diagnostic mammograms are not considered a preventative service, so your Part B or Medicare Advantage plan coinsurance and deductible will most likely apply.