Your Medicare Part B and Part D premiums are not determined by "total gross income." They are determined by your Modified Adjusted Gross Income (MAGI). As others have said, MAGI for increased Medicare premiums ("IRMAA") is your Adjusted Gross Income (AGI) plus tax-exempt interest. For 2020, 2021, and 2022 AGI is Form 1040 line 11 and tax-exempt interest is Form 1040 line 2a, so you just add those two lines together.
Keep in mind that your premiums are based on your MAGI from two or three years ago. For example, your premiums for 2024 will usually be based on your 2022 tax return, or possibly your 2021 tax return.
