How does roth conversion tax bracket planning work, and how do I fill the right brackets before RMDs hit?

Roth conversion tax bracket planning is the practice of converting traditional IRA or 401(k) dollars to a Roth IRA in amounts deliberately sized to fill specific federal tax brackets each year — typically the 12% and 22% brackets (and sometimes 24%) — so that money is taxed at rates lower than what you would otherwise pay later, either through required minimum distributions (RMDs) starting at age 73 or through higher future tax rates. Done well, it can save six figures over a retirement. Done carelessly, it can cost you thousands in unnecessary taxes, Medicare IRMAA surcharges, and lost subsidies. Here is how the strategy actually works in 2026 and how to execute it without stepping on landmines.

The Direct Answer: Fill Low Brackets Before RMDs Force High Ones

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The core logic of roth conversion tax bracket planning comes down to arbitrage between your tax rate today and your expected rate later. Most retirees between roughly age 60 and 73 have unusually low taxable income: they are no longer earning a salary, Social Security may not have started yet, and RMDs do not begin until age 73 (age 75 for those born in 1960 or later). That creates a window where large portions of income can be converted at the 12%, 22%, or 24% marginal rates. Once RMDs begin, a retiree with a large traditional balance may be pushed into the 22%, 24%, or even higher brackets every single year for life — plus higher Medicare premiums via IRMAA and up to 85% of Social Security benefits becoming taxable.

Consider a concrete illustration drawn from real-world planning cases reported in 2025–2026: a married couple, both 62, with $700,000 in traditional retirement accounts and modest current income. By converting roughly $90,000–$100,000 per year for seven years — staying within the top of their planned bracket each year — they could eliminate an estimated $160,000 in projected lifetime taxes that would otherwise come from RMDs stacking on top of Social Security. A similar case involves a 59-year-old with $1.3 million in a 401(k) converting about $130,000 annually to avoid RMD-driven bracket creep. These are not exotic tricks; they are arithmetic applied consistently over a decade.

The key phrase to internalize is 'fill the bracket.' If the top of the 22% bracket for a married couple filing jointly sits around $206,700 of taxable income in 2026, and your ordinary taxable income is $60,000, you have roughly $146,000 of bracket room available for conversions before you spill into the 24% bracket. Converting exactly that amount — no more, no less — is the discipline. Conversions above the target bracket get taxed at the next rate up, which erodes the math quickly.

Why the Math Works: Rate Arbitrage and Bracket Smoothing

Traditional accounts defer taxes; Roth accounts eliminate them on qualified growth. A conversion simply moves money from the deferred-tax bucket to the never-again-taxed bucket, paying the bill now instead of later. The strategy wins when three conditions hold. First, your marginal rate this year is below your expected marginal rate in future withdrawal years. Second, you have outside funds to pay the conversion tax — paying the tax from the conversion proceeds themselves reduces the amount actually moved into the Roth and weakens returns. Third, you have enough years before RMDs (or before death, if leaving assets to heirs) for tax-free compounding to matter.

Bracket smoothing is the second engine of savings. A retiree who takes $0 from investments until 73, then suddenly withdraws $80,000+ per year under RMD rules, experiences wildly lumpy taxation: near-zero tax in early retirement, then permanently elevated brackets afterward. Because the U.S. system is progressive with wide brackets, spreading income evenly across 20 years often produces less total tax than concentrating it into 15. Conversions let you manufacture even income during the gap years, effectively prepaying RMDs at controlled rates.

There is also an estate dimension. Heirs who inherit traditional IRAs must generally empty them within 10 years under the SECURE Act's post-death distribution rules, and distributions count as their ordinary income. A 45-year-old daughter inheriting a $500,000 traditional IRA while earning a good salary could lose 32%–35% of it to taxes. Inherited Roth dollars carry no such problem. For families planning wealth transfer, conversion rates as high as 30%+ can still beat the heir's likely rate.

The Practical Steps: How to Actually Run a Conversion Plan

Step one is building a year-by-year projection of taxable income from now through roughly age 80, including Social Security claiming ages, pension income, portfolio withdrawals, and projected RMDs. This projection tells you which years are 'low-bracket years' worth filling and which years are already full. Software tools — including AI-assisted financial advisors and simulators like those built by independent planners — can automate thousands of these scenarios; a competent fee-only advisor or CPA can do the same manually. The output should be a target conversion dollar amount per year, matched to a specific bracket ceiling.

Step two is checking the thresholds that sit just above the brackets. Medicare IRMAA surcharges trigger at modified AGI above roughly $109,000 for singles and $218,000 for couples (2026 figures, based on two-year lookback), adding hundreds to thousands per person per year in Part B and D premiums. ACA marketplace premium subsidies, if applicable, disappear sharply above specific income levels. Conversions also count as income for capital gains purposes, potentially pushing long-term gains out of the 0% bracket. Your conversion target must be set net of all of these cliffs, not just the income tax brackets.

Step three is execution mechanics. Conversions can be done anytime before December 31 of the tax year — there is no deadline tied to April 15 except for recharacterization decisions (and note that recharacterizations were eliminated after 2017, so conversions are irreversible). Many planners split conversions across the year or do them late in the year once actual income is known. You will owe tax at filing time since conversions have no withholding requirement, though voluntary withholding or estimated payments avoid penalties. Each conversion is permanent, so model carefully before pulling the trigger.

Conversion Planning Compared: Doing Nothing vs. Filling Brackets vs. Maxing Out

The table makes the tradeoff visible: doing nothing is only defensible when balances are small enough that RMDs stay inside low brackets anyway. Full liquidation of a traditional account in a few years usually backfires because the final chunks get taxed at 32%–37%. Bracket-filling is the middle path that captures most of the benefit at a controlled cost. Notably, some economists — Laurence Kotlikoff among them — argue that formulaic 'convert every year' advice pushed by financial media can destroy value when it ignores a household's actual lifetime tax picture; the plan must be modeled, not templated.

Common Mistakes That Turn a Good Strategy Into an Expensive One

The most frequent error is ignoring IRMAA. A couple converting $250,000 in a single year at age 63 will see Medicare premiums jump two years later, potentially wiping out much of the bracket savings. Related to this is converting too much in one year rather than spreading across several — the progressive bracket structure rewards patience. A third mistake is paying conversion taxes from IRA proceeds instead of a brokerage account, which shrinks the tax-free base exactly where compounding matters most.

Another common failure is forgetting state taxes. States like California, New York, and New Jersey fully tax conversions at resident rates, which can add 5%–10% to the true cost. Retirees planning to move from a high-tax state to Florida or Texas face a timing decision: convert before moving and pay the high state rate, or move first and convert tax-free. Conversely, someone moving to a high-tax state should convert beforehand. Finally, many people convert without modeling survivor outcomes — a surviving spouse filing single faces narrower brackets and higher rates, which changes the optimal conversion schedule materially.

One more subtle trap: conversions increase AGI, which affects ACA subsidy eligibility for pre-65 retirees, the taxation of Social Security benefits (via combined income calculations), and investment income thresholds. A conversion that saves 4 points of bracket can simultaneously cost more than that in lost premium tax credits. Every dollar figure needs to be checked against the full stack of interacting thresholds.

When to Act: Timing Windows That Close

The prime conversion window runs from retirement (or semi-retirement) until RMDs begin at 73, with special urgency in the two years before Medicare enrollment at 65 because IRMAA lookback means income at 63–64 sets premiums at 65+. Planners frequently describe the 60-to-65 stretch as a window that closes the day Medicare starts. After 65, conversions remain viable but must be sized against IRMAA tiers; after 73, conversions stack on top of mandatory RMDs, raising the effective cost.

Calendar-year timing also matters. Conversions must be completed by December 31 to count for that tax year. Late-year execution — say November or December, once year-end bonuses, capital gains, and business income are known — lets you fill the bracket precisely. Some taxpayers deliberately wait until December to convert, then use the December 31 deadline as a hard stop. Tax-law uncertainty cuts both ways: the individual rate schedule currently in place is scheduled to change after 2025 legislation sunsets in future years, and TCJA-era rates were already historically low, which argues for capturing 22%–24% rates while they exist rather than betting on them persisting.

Costs, Tools, and Whether You Need an Advisor

Conversions themselves are free at most brokerages — Vanguard, Fidelity, Schwab all process them online with no transaction fee. The real costs are the taxes themselves and the advisory fees to plan correctly. A flat-fee or hourly planner might charge $1,500–$5,000 for a one-time conversion analysis; comprehensive ongoing planning runs $2,500–$10,000 annually or roughly 0.5%–1% of assets under management. DIY software options range from free calculators to subscription simulators costing $100–$500 per year, and newer AI-driven planning tools can stress-test conversion schedules against market scenarios automatically.

Whether professional help pays for itself depends on complexity. A single retiree with one IRA and simple income can self-plan with a spreadsheet and IRS tax tables. Households juggling pensions, Social Security timing, rental property, state moves, ACA coverage, and seven-figure balances almost always benefit from modeling software or a fee-only advisor, because the interaction effects (IRMAA, NIIT, subsidy cliffs, survivor analysis) routinely shift optimal conversion amounts by tens of thousands of dollars per year. Given that a well-executed decade-long plan can save $100,000–$200,000 in lifetime taxes, a few thousand in planning fees is usually cheap insurance — but verify any advisor's recommendation against your own numbers rather than accepting a generic 'convert $X per year' rule.

Bottom Line

Roth conversion tax bracket planning works because it exploits a temporary mismatch: low-income gap years between retirement and RMDs versus structurally higher forced-income years afterward. Fill the 12%–24% brackets methodically each year from roughly 60 to 73, pay the tax from outside funds, respect the IRMAA and subsidy cliffs sitting just above each threshold, and model the survivor scenario before committing. Spread conversions across many years rather than a few, complete them by December 31, and revisit the plan annually as tax law and your income evolve. Executed with that discipline, the strategy reliably converts a future tax liability into a controlled, discounted payment — executed casually, it can hand the IRS more money than doing nothing at all.