Per IRS Publication 17, Tax Guide for Individuals, page 159:

Medicare A

If you are covered under social security (or if you are a government employee who paid Medicare tax), you are enrolled in Medicare A. The payroll tax paid for Medicare A isn't a medical expense.

If you aren't covered under social security (or weren't a government employee who paid Medicare tax), you can voluntarily enroll in Medicare A. In this situation, you can include the premiums you paid for Medicare A as a medical expense.

Medicare B

Medicare B is supplemental medical insurance. Premiums you pay for Medicare B are a medical expense. Check the information you received from the Social Security Administration to find out your premium.

Medicare D

Medicare D is a voluntary prescription drug insurance program for persons with Medicare A or B. You can include as a medical expense premiums you pay for Medicare D.

See IRS Publication 17 Your Federal Income Tax (For Individuals) for more information.

To enter or review information from Form SSA-1099, including Medicare Parts B and D premiums:

1. From within your TaxAct® return (Online or Desktop), click Federal. On smaller devices, click in the upper left-hand corner, then select Federal.
2. Click Social Security Benefits in the Federal Quick Q&A Topics menu
3. The program will proceed with the interview questions for you to enter or review the appropriate information

To enter Medicare Parts B and D premiums not reported on Form SSA-1099:

1. From within your TaxAct return (Online or Desktop) click Federal. On smaller devices, click in the upper left-hand corner, then select Federal.
2. Click Itemized or Standard Deductions to expand the section, then click Medical and dental expenses in the Federal Quick Q&A Topics menu
3. The program will proceed with the interview questions for you to enter the applicable information