No, Medicare B premiums don’t count as income, per se.
However, the amount in Box 5 of your Form SSA-1099 – including Medicare B premiums, if present – is used in the computation of the taxable Social Security amount included on your return.
Please see the Social Security Benefits Worksheet—Lines 6a and 6b on page 31 of the 2021 Instructions for Form 1040 to see how taxable Social Security benefits are computed using Box 5.
