@rusty1992
MAGI is calculated differently for different purposes. There are about a dozen different ways to calculate MAGI, depending on what it's being used for. TurboTax does not calculate MAGI for IRMAA because it is not used on a tax return. Any MAGI calculations in TurboTax are for other purposes, and are calculated differently.
MAGI for IRMAA is simply AGI plus tax-exempt interest. On your 2020, 2021, or 2022 tax return, the MAGI for IRMAA is Form 1040 line 11 plus line 2a. But your IRMAA is based on your MAGI from two or three years ago. For example, your IRMAA for 2023 will usually be based on your 2021 tax return, or possibly your 2020 tax return.
