A: If you are talking about an increase that was greater than the yearly cost-of-living increase, then you probably ran into IRMAA, otherwise known as the income-related monthly adjusted amount. Medicare’s Part B and Part D premiums are based on your modified adjusted gross income as reported on your IRS tax return from 2 years ago. This is the most recent tax return information provided to Social Security by the IRS. If your income exceeded a certain amount, you will pay a higher premium. An event like the sale of securities can place you into a different category and trigger a higher premium for either Part B or Part D, or both. The good news is that since IRMAA is calculated every year, you will not have to pay the adjustment the next year if your income falls below the threshold.