How can I know whether I’ll be subject to the Medicare surcharge next year?

Medicare beneficiaries with modified adjusted gross income (MAGI) over a set amount ($85,000 for single individuals and $170,000 for married persons filing jointly) pay an additional Part B and Part D premium. MAGI in 2017 is what is used to determine whether there’s an additional premium in 2019. MAGI for this purpose means your adjusted gross income plus tax-exempt interest income.