Remember the two-year lookback!
Medicare looks at income (in the form of MAGI - Modified Adjusted Gross Income) from two tax years prior to determine the Part B/D Premium IRMAA adjustments. There are multiple calculations for MAGI based on the planning application, but for Medicare Part B/D Premium purposes, MAGI is equal to:
Adjusted Gross Income (AGI) + Tax-Exempt Interest
A taxpayer's MAGI from 2023 will impact Medicare Part B/D Premiums in 2025. That impact is for one tax year only. For example, 2023 income affects 2025 Medicare Part B/D Premiums, and only for 2025, not any other calendar years. This can be challenging to plan around, since income this year affects Medicare Part B/D Premiums two years from the current year, and those Medicare Part B/D Premiums and MAGI thresholds two years from now aren't official.
Remember, even though your clients may not be eligible for Medicare, their income this year could impact Medicare Premiums in the future if they are within two years from becoming a Medicare participant! Therefore, generally beginning at age 63, you will want to pay attention to your client's income to gauge if any planning done in that year will impact the amount they pay for Medicare Part B/D Premiums.
You can see these IRMAA income thresholds and associated IRMAA surcharges for Medicare Parts B and D on the Tax Report, within the "MAGI" section of Scenario Analysis, or within our Range Calc tool.
Though the amount of the surcharges and MAGI bracket amounts for each threshold have not been published yet by the federal government for years beyond 2025, Holistiplan defaults to leaving the dollar amounts of the surcharges and MAGI brackets at the currently published amounts to be more conservative, particularly because once you have exceeded a given threshold - even by $1 - any Medicare participants on the return are subject to that next IRMAA surcharge.
If you would rather not use the more conservative default setting to use the most current numbers, you can elect to inflate those MAGI brackets by checking the box highlighted below in Scenario Analysis. 
NOTE: This checkbox does NOT impact the tax calculation itself. Instead, it impacts the Medicare and MAGI phaseout information in the Tax Report and in the section at the bottom of this screen. It also impacts the placement of the Medicare IRMAA brackets depicted on the Range Calc screen, and impacts the Medicare thresholds referenced in the Solve for Max calculator on this screen.
The Centers for Medicare and Medicaid Services publishes numbers for the following year each year, generally in September or October. When the new numbers are published, updated numbers will be incorporated within Holistiplan.
If you have any questions, or we can provide additional clarity on how Medicare Part B/D Premium IRMAA adjustments are handled within Holistiplan, please feel free to reach out to our Support Team for more assistance!