Yes, you can do a partial Roth conversion, and it is how most retirees approach the strategy. The IRS sets no minimum and no maximum, so a Roth conversion is not all-or-nothing. You choose the amount each year, size it to a target tax bracket, and repeat before required minimum distributions begin at age 73.
Yes. You can convert any amount from a traditional IRA or 401(k) to a Roth in a given year, from a small slice to the full balance. The IRS places no floor and no cap, and the converted pre-tax amount is added to your ordinary income for that year. (Source: IRS, Retirement Plans FAQs Regarding IRAs, 2026.)
Can you do a partial Roth conversion?
Yes. The IRS treats the converted amount as your choice, not a fixed all-or-nothing transfer, and sets no required minimum and no annual maximum. That differs from the contribution limits that cap Roth IRA deposits at $7,500 ($8,600 if age 50 or older) in 2026. A conversion also has no income limit. (Source: IRS, 2026 limits release.)
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Because a conversion is not all-or-nothing, you decide the amount, your custodian moves it to a Roth IRA, and the pre-tax dollars become ordinary income for the year. Money inside the Roth then grows tax-free, and there are no owner-lifetime RMDs. Partial conversions keep each year’s tax cost inside a bracket you accept. See the Q3 overview of Roth conversion planning.
This guide focuses on the math. For a decision-focused look at where the strategy helps or backfires, see the companion guide on when partial Roth conversions work and when they don’t.
How is a partial Roth conversion taxed?
The converted pre-tax amount is taxed as ordinary income in the conversion year and stacks on your other income. There is no early-withdrawal penalty on the conversion itself. If you hold after-tax basis, the pro-rata rule taxes it proportionally across all your traditional, SEP, and SIMPLE IRAs, reported on Form 8606. (Source: IRS Form 8606 instructions, 2025.)
A conversion is a taxable event, added to your adjusted gross income and taxed at ordinary rates. You cannot convert a required minimum distribution, so once RMDs begin you take the RMD first.
Does the pro-rata rule apply across all my IRAs?
Yes, if you have ever made non-deductible (after-tax) contributions to a traditional IRA. Under IRC 408(d)(2), the IRS treats all your traditional, SEP, and SIMPLE IRAs as one pool when it figures the taxable portion, reported on Form 8606, so you cannot convert only the after-tax basis. One exception: workplace 401(k) and TSP balances are not part of that aggregation.
How much of my IRA should I convert this year?
A common method is bracket-filling: find where your current federal bracket ends, subtract your projected taxable income, and convert up to that gap. For 2026 married-filing-jointly returns, the 12% bracket ends at $100,800 of taxable income and the 22% bracket ends at $211,400. (Source: IRS Rev. Proc. 2025-32 / Tax Foundation, 2026.)
The method takes three steps:
- Estimate your projected taxable income net of the 2026 standard deduction ($32,200 for joint filers, plus $1,650 per spouse age 65 or older).
- Identify the top of the bracket you are willing to fill.
- Subtract your income from that ceiling to find the amount you could convert at or below that rate.
The table below uses a hypothetical joint filer with $70,000 of taxable income.
| Target ceiling (2026 MFJ) | Ceiling (taxable income) | Income before conversion | Room to convert this year |
|---|---|---|---|
| Top of 12% bracket | $100,800 | $70,000 | $30,800 |
| Top of 22% bracket | $211,400 | $70,000 | $141,400 |
Q3 Advisors covers this in its guide on how much to convert to a Roth.
A bracket-filling example (multi-year, hypothetical)
Consider a hypothetical married couple, both age 66, in a gap year, with about $70,000 of taxable income and roughly $200,000 to move to a Roth over time. The table compares spreading it over five years against doing it all at once.
| Approach | Per year | Approx. taxable income that year (MFJ) | Highest bracket reached | Trade-off |
|---|---|---|---|---|
| Spread: $40,000 per year for 5 years | $40,000 | ~$110,000 | 22% | Upper dollars capped at 22%; more control over IRMAA and ACA thresholds each year |
| Lump sum: $200,000 in one year | $200,000 | ~$270,000 | 24% | Moves the balance out faster, but upper dollars are taxed at 24% and one year’s MAGI spikes |
Spreading the $200,000 across five years keeps each year’s top dollars in the 22% bracket, while the lump sum pushes the upper slice into 24% and spikes one year’s MAGI. Neither is universally right; it depends on your future bracket, balances, and the hidden costs below.
What does a conversion really cost? Your true marginal rate
Your federal bracket rarely tells the whole story. A conversion can also raise Medicare IRMAA surcharges, cost part of an ACA premium tax credit, increase the taxable share of Social Security benefits, expose investment income to the 3.8% Net Investment Income Tax, and add state tax. Together these can push the true marginal cost well above the stated bracket.
Each row below is a separate rule with its own threshold.
| Cost layer | 2026 trigger point | How it affects a conversion |
|---|---|---|
| Federal ordinary bracket | 22% starts $100,800; 24% starts $211,400 (MFJ) | The stated marginal rate on each converted dollar. |
| Medicare IRMAA (Part B and D) | MAGI above $109,000 single / $218,000 joint | Crossing a tier lifts the Part B premium above the $202.90 standard amount, plus a Part D surcharge. Two-year lookback: a 2026 conversion can affect 2028 premiums. (Source: CMS, 2026.) |
| ACA premium tax credit | Income-based; under-65 marketplace coverage | Extra conversion income can reduce or end a marketplace premium subsidy. |
| Social Security taxation | Up to 85% of benefits become taxable | Added income can pull more of your benefit into taxable income, sometimes called the tax torpedo. (Source: IRS Pub. 915.) |
| Net Investment Income Tax | MAGI above $200,000 single / $250,000 joint | A 3.8% tax on net investment income can apply once conversion income lifts MAGI over the threshold. The conversion itself is not net investment income, but it raises the MAGI that exposes other income. (IRC 1411.) |
| State income tax | Varies by state | Most states tax the converted amount as ordinary income; a handful do not tax retirement income. |
A conversion sized only to a federal bracket can still trip an IRMAA tier, a subsidy phase-out, or the Social Security stacking effect, so timing matters as much as amount.
When does a partial Roth conversion make sense?
Partial conversions are most often examined during the gap years between retirement and RMD age (roughly 60 to 73), in low-income years, after a market decline, and when a saver expects higher future tax rates. Converting before RMDs begin at 73 also shrinks the pre-tax balance that drives required distributions. (Source: IRS RMD FAQs, 2026.)
Several situations tend to make partial conversions worth analyzing. None guarantees a benefit.
- Gap years before RMDs. Between the end of paid work and RMD age 73 (rising to 75 for those born in 1960 or later, first applying in 2035), income is often lower.
- Low-income years. Reduced wages, a business loss, or large deductions can open bracket space.
- After a market decline. When values fall, a set dollar conversion moves more shares for the same tax cost, and any recovery happens inside the Roth.
- Higher future rates. The 37% top rate is now permanent, but future legislation or your own income can still raise your bracket.
- RMD reduction. Every dollar converted before 73 leaves the pre-tax balance that drives future required minimum distributions.
- Estate planning. Under the SECURE Act, many non-spouse heirs must empty an inherited IRA within 10 years; a Roth inheritance is generally income-tax-free to them.
The survivor and widow single-filer squeeze
When one spouse dies, the surviving spouse usually files as single the next year, and single brackets compress the same income into higher rates. The single standard deduction is $16,100 in 2026 versus $32,200 for joint filers, so a widowed retiree loses roughly half the deduction while keeping most of the income. Converting while both spouses are alive and filing jointly is one way couples examine spreading tax before that compression.
What are the pitfalls?
Key pitfalls include the per-conversion five-year clock (each conversion starts its own, with penalty exposure under age 59.5), the fact that conversions cannot be reversed since 2018, IRMAA’s two-year lookback, over-converting into the next bracket, and paying the tax from the IRA itself. (Sources: IRS Pub. 590-B; IRS FAQs, 2026.)
- The per-conversion five-year clock. Each conversion starts its own five-year clock; withdrawing converted principal before five years pass and before age 59.5 can trigger the 10% penalty on that amount, so a ladder has multiple overlapping clocks. (Source: IRS Pub. 590-B, 2025.)
- You cannot undo it. Recharacterizing (reversing) a conversion has been prohibited since January 1, 2018 under the Tax Cuts and Jobs Act; the last reversible conversions were 2017.
- The IRMAA two-year lookback. A surcharge can appear two years later, so a 2026 conversion may raise 2028 Medicare premiums. The last conversion year that does not affect a premium is age 62.
- Over-converting. Mis-estimating year-end income can push a few dollars into the next bracket or across an IRMAA tier.
- Paying the tax from the IRA. Using IRA dollars for the tax shrinks what reaches the Roth and, under 59.5, can add a penalty on the withheld portion.
How do I execute a partial Roth conversion?
You tell your custodian how much to move from the traditional IRA to a Roth IRA, ideally trustee-to-trustee. The conversion must be completed by December 31, unlike contributions, which allow an April window. Your custodian issues Form 1099-R, and you report the conversion on Form 8606. (Source: IRS Form 8606 instructions, 2025.)
- Decide the dollar amount using the bracket and cost-stack analysis above.
- Instruct your custodian to move that amount to a Roth IRA, preferably by trustee-to-trustee transfer.
- Complete the conversion by December 31; there is no prior-year window as there is for contributions. See the Q3 note on the 2026 Roth conversion deadline.
- Pay the income tax from non-retirement funds so the whole converted amount stays invested.
- Report the conversion on Form 8606; your custodian sends Form 1099-R documenting the distribution.
Converting from a 401(k) or TSP
You can move workplace dollars to a Roth, but the path differs by plan. Some 401(k) and TSP plans allow an in-plan Roth conversion or a direct rollover to a Roth IRA; others require you to leave the employer or reach a plan-defined age first. Either way, the pre-tax amount moved to Roth is ordinary income that year. Plan balances sit outside IRA aggregation, so they do not affect an IRA conversion’s pro-rata math.
Is a partial Roth conversion still worth it after OBBBA?
The rationale shifted rather than disappeared. The One Big Beautiful Bill Act (P.L. 119-21, signed July 4, 2025) made the TCJA income tax rates permanent, so the old “convert before rates rise in 2026” urgency is gone. Many retirees now weigh conversions for RMD reduction, the survivor single-filer squeeze, and tax-free inheritance.
With the 10% through 37% brackets now permanent, no scheduled rate increase forces a decision. The reasons to consider a partial conversion are structural: lowering future required minimum distributions, avoiding the compressed single-filer brackets a surviving spouse faces, and passing tax-free dollars to heirs. OBBBA also added a temporary senior deduction of $6,000 per person age 65 or older for 2025 through 2028.
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Q3 Advisors is a registered investment adviser focused on retirement tax planning. This page is educational and is not advice; consult a qualified professional.
Frequently asked questions
Can you do a partial Roth conversion?
Yes. A partial Roth conversion is fully allowed, and it is how most retirees use the strategy. The IRS sets no minimum and no maximum on the amount you convert in a year, so you can move a small slice or a large one. The converted pre-tax amount counts as ordinary income for that tax year. (Source: IRS FAQs, 2026.)
Is there a limit on how much you can convert to a Roth in one year?
No. Unlike Roth IRA contributions, which are capped at $7,500 ($8,600 if age 50 or older) and phase out for joint filers between $242,000 and $252,000 of MAGI in 2026, a conversion has no dollar limit and no income limit. Larger conversions simply push more income into higher brackets. (Source: IRS, 2026 limits.)
How much of my IRA should I convert to a Roth each year?
A common method is bracket-filling: convert up to the top of a chosen federal bracket. For 2026 joint returns, the 12% bracket ends at $100,800 and the 22% ends at $211,400 of taxable income. Subtract your projected income from that ceiling to find the room, then check IRMAA and Social Security effects. (Source: Tax Foundation, 2026.)
Does a partial Roth conversion make sense?
It often makes sense during the gap years between retirement and age 73, in low-income years, after a market decline, or when you expect higher future tax rates. It can also shrink future required minimum distributions and leave tax-free money to heirs. Whether it fits depends on your brackets and Medicare timing. (Source: IRS, 2026.)
At what age does a Roth conversion not make sense?
There is no fixed age when a conversion stops making sense, but the window narrows once RMDs begin at 73 and Medicare IRMAA’s two-year lookback applies. The last conversion year that does not affect a Medicare premium is age 62. Later conversions can still help heirs. (Source: CMS, 2026.)
How do I avoid paying taxes on a Roth conversion?
You cannot avoid the tax entirely; converting pre-tax dollars is always ordinary income in the conversion year. You can reduce it by converting in low-income years, spreading the amount across several years, converting after a market decline, and paying the tax from non-retirement cash. (Source: IRS Pub. 590-B.)
Is it better to convert all at once or over several years?
Neither is universally better. Spreading conversions over several years keeps each year’s income in lower brackets and away from IRMAA thresholds, while a single large conversion moves more out of the pre-tax balance sooner but taxes the upper dollars at higher rates. The right split depends on account size, age, and expected future rates.
Will a Roth conversion increase my Medicare premiums?
It can. Medicare IRMAA raises Part B and Part D premiums once modified adjusted gross income crosses a tier, with the first 2026 tier above $109,000 single and $218,000 joint. IRMAA uses a two-year lookback, so a 2026 conversion can raise 2028 premiums. The standard 2026 Part B premium is $202.90 per month. (Source: CMS, 2026.)
