Can timing or splitting Roth conversions across tax years reduce IRMAA impacts in 2025–2026?
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Executive summary
Timing and splitting Roth conversions can materially change Medicare IRMAA outcomes because IRMAA is calculated from MAGI two years earlier; a conversion in 2025 affects premiums in 2027, and a 2026 conversion affects 2028 (sources explain the two‑year lookback and examples) [1] [2] [3]. Financial advisors and outlets recommend spacing conversions to stay inside tax brackets and avoid pushing MAGI above IRMAA thresholds; the surcharge ranges for 2025 show annual Part B increases from hundreds to several thousand dollars depending on bracket [4] [5].
1. Why the calendar matters: the two‑year MAGI “lookback”
Medicare’s IRMAA uses your modified adjusted gross income from the tax return filed two years prior, so any Roth conversion that raises MAGI in year X is what Medicare will use for premiums in year X+2; several planning pieces spell this out and warn that a large 2025 conversion could increase Part B/D premiums in 2027 [4] [2] [3].
2. The basic tradeoff: taxes now versus Medicare surcharges later
Roth conversions produce taxable income in the year of conversion; that added MAGI can push you into higher IRMAA tiers and cost hundreds to thousands annually in Part B and D surcharges. Kiplinger quantifies 2025 extra Part B costs ranging from about $888 to $5,326.80 per year and Part D from about $164.40 to $1,029.60 depending on how far MAGI exceeds thresholds [4]. Planning must weigh the immediate tax bill against both long‑term tax savings and any temporary Medicare premium hit [6] [3].
3. Splitting conversions across years: how it can lower IRMAA exposure
Multiple sources recommend laddering or spacing conversions so a single year’s MAGI doesn’t breach an IRMAA threshold or a higher tax bracket; spreading a large conversion over 2025 and 2026 can reduce the chance one conversion year creates a two‑year‑later IRMAA cliff [7] [8] [9]. Northern Trust and other planners model conversions over several years to minimize combined tax plus IRMAA costs and to avoid “bunching” that pushes filers into costly brackets [9] [10].
4. Timing windows and law changes in 2025–2026 complicate decisions
Recent and pending law changes (discussed in OBBBA analyses) and projected tax‑bracket shifts for 2026 make conversion timing more consequential: some advisers argue converting in 2025 could be preferable to 2026 because of how other deductions and rules interact, but the optimal year depends on your full tax picture [2] [9] [11]. Available sources note that conversions in 2025–2026 interact with SALT, charitable deduction changes, and shrinking brackets — all of which can change both tax and IRMAA math [12] [9].
5. Tactical levers planners use to manage IRMAA risk
Advisors cite several practical moves: convert only up to the top of your current tax bracket, split large conversions over multiple tax years, use charitable deductions or qualified charitable distributions to offset taxable income, and model scenarios with a CPA to see IRMAA impacts for specific dollar amounts [8] [7] [6]. Sources caution that conversions must be completed in the calendar year to count for that year’s MAGI and that TSP and other plan timing changes (Roth in‑plan conversions starting 2026) also affect planning logistics [13] [14].
6. Where uncertainty and disagreement remain
Writers and forums differ on the size of the IRMAA penalty that justifies avoiding a conversion and on whether it’s better to “bite the bullet” before 2026 tax changes or delay — examples and models show different outcomes depending on SALT, NIIT, itemized deductions and future bracket assumptions [12] [11] [9]. Some analysis notes IRMAA affects only roughly 8% of enrollees, so for many retirees the Medicare surcharge is not the dominant factor [15]; others emphasize high‑net‑worth scenarios where IRMAA plus NIIT and deduction phaseouts can push effective rates very high [12] [5].
7. Practical next steps — what the sources recommend you do now
Run concrete scenarios with a tax pro: model how specific conversion amounts in 2025 versus 2026 change taxable income, tax brackets, and projected IRMAA premiums two years later; consider splitting conversions across years to keep annual MAGI under IRMAA cliffs and “fill up” a bracket rather than jumping to the next [8] [9] [5]. If you use employer plans like the TSP, factor in in‑plan conversion rules coming in 2026 and the requirement to use outside funds to pay conversion taxes [13] [14].
Limitations and sourcing note: this analysis draws only on the provided reporting and planning pieces, which consistently state IRMAA is based on MAGI two years prior and that conversions count as taxable income the year performed; available sources do not mention individualized IRS or SSA rulings that might change application to a particular taxpayer [4] [3] [2].