Roth conversion and capital gains stacking is the ordering rule that decides how much a conversion really costs in a given tax year: the taxable part of the conversion is ordinary income that fills your tax brackets first, and your long-term capital gains and qualified dividends stack on top of it. When conversion income raises your taxable income, gains that would have been taxed at 0% can be repriced to 15% or 20%, so the two moves have to be planned together, not separately.
A Roth conversion is ordinary income (IRS Pub 590-B) and stacks below long-term capital gains and qualified dividends, which are taxed at 0%, 15%, or 20% based on total taxable income. In 2026 the 0% rate ends at $98,900 taxable income for married filing jointly and $49,450 for single filers (Rev. Proc. 2025-32). A conversion that fills that space can reprice otherwise-0% gains into the 15% band.
How does a Roth conversion and capital gains share the same bracket space?
A Roth conversion and capital gains share the same bracket space because federal tax stacks income in a fixed order: ordinary income is taxed first, and long-term capital gains and qualified dividends are calculated on top of it. The taxable portion of a Roth conversion is ordinary income, so it occupies the lower brackets before your preferential-rate income is measured. That ordering follows the IRS capital gains worksheet (Source: IRS Topic No. 409).
Talk With Craig Wear's Team
Craig has helped IRA millionaires save over $1 million each in unnecessary taxes. Find out if a Roth conversion strategy fits your retirement, with no sales pressure and no product pitch.
The practical result is a competition for one slice of bracket room. In a low-income “gap year” before required minimum distributions or Social Security begin, a household may have space beneath the 0% capital gains ceiling. A conversion and a gain harvest both want that space, and the dollars a conversion consumes are dollars no longer available at the 0% gains rate.
Because the conversion sits underneath, it never receives preferential rates itself. It is taxed in the ordinary brackets and, by raising taxable income, it lifts the starting point at which your gains are measured (Source: IRS Pub 590-A; Instructions for Form 8606). Deciding how large a conversion to run is part of a broader how much to convert to a Roth analysis.
Why can a conversion turn 0% gains into 15% gains?
Long-term gains stay at 0% only while total taxable income sits at or below the zero-rate ceiling. When a Roth conversion adds ordinary income, it raises total taxable income, and any gains sitting above the new, higher total are taxed at 15% instead of 0% (Source: IRS Topic No. 409). The gain did not change; the income beneath it did.
This creates a hidden marginal cost. A conversion dollar taxed in the 12% ordinary bracket can also push one dollar of gain from 0% to 15%, so the true marginal rate on that layer approaches 27% (12% plus 15%), even though the tax table shows only 12%. Quantifying that repricing is part of any Roth conversion break-even estimate.
What are the 2026 capital gains breakpoints that govern the decision?
The 0%, 15%, and 20% long-term capital gains rates are set by taxable-income breakpoints that change each year. For 2026 they come from IRS Rev. Proc. 2025-32. These thresholds define exactly how much combined room exists for conversion income and gains before the next rate tier begins, so they anchor every stacking decision.
| Filing status (2026) | 0% rate up to | 15% rate up to | 20% rate above |
|---|---|---|---|
| Married filing jointly / surviving spouse | $98,900 | $613,700 | $613,700 |
| Single | $49,450 | $545,500 | $545,500 |
| Head of household | $66,200 | $579,600 | $579,600 |
| Married filing separately | $49,450 | $306,850 | $306,850 |
Source: IRS Rev. Proc. 2025-32, section 4.03 (2026 maximum capital gains rate amounts).
These are taxable-income figures, measured after deductions, not gross income. Both the conversion and the gains count toward the same taxable-income total that is compared against each ceiling, which is why they cannot be planned in isolation.
How do the 2025 breakpoints compare?
The 2025 breakpoints are lower, so a taxpayer completing a conversion in 2025 has slightly less 0% room than in 2026. For 2025 the 0% ceiling is $96,700 for married filing jointly and $48,350 for single filers (Source: IRS Topic No. 409; Rev. Proc. 2024-40). Most articles still quote these 2025 figures, so confirming the current-year number matters before you model a conversion.
| Filing status | 2025 0% ceiling | 2026 0% ceiling |
|---|---|---|
| Married filing jointly | $96,700 | $98,900 |
| Single | $48,350 | $49,450 |
| Head of household | $64,750 | $66,200 |
Sources: IRS Topic No. 409 and Rev. Proc. 2024-40 (2025); Rev. Proc. 2025-32 (2026).
Does a Roth conversion count as a capital gain?
No. A conversion of a traditional IRA to a Roth IRA is included in gross income for the year received and is taxed in the ordinary-income brackets, not at capital gains rates (Source: IRS Pub 590-A and Pub 590-B). The taxable amount is reported on Form 8606 and flows to Form 1040 line 4b. It never qualifies for the 0%, 15%, or 20% preferential long-term rates.
This distinction explains why the conversion sits beneath your gains rather than beside them. Ordinary income, including converted amounts, is stacked first, and only genuine long-term capital gains and qualified dividends receive preferential treatment (Source: IRS Topic No. 409).
There is also no income limit on Roth conversions. The pre-2010 $100,000 MAGI cap was permanently repealed, so a conversion is available at any income level, unlike Roth contributions, which phase out between $242,000 and $252,000 of MAGI for married filing jointly in 2026 (Source: IRS Pub 590-A). A conversion is uncapped, taxable, irreversible, and must be completed by December 31.
Should I do a Roth conversion or harvest capital gains at 0% in the same year?
When bracket room is limited, a household usually cannot both convert to a Roth and harvest gains at 0% up to the full ceiling, because both draw on the same taxable-income budget. Neither choice is universally better. One practical framing is to size the room beneath the 0% ceiling first, then decide how many of those dollars to spend on conversion income versus tax-free gain harvesting.
This page focuses on the stacking mechanics; for the side-by-side tradeoff, see Roth conversion vs capital gain harvesting.
A dollar used for a conversion is taxed at your ordinary rate on that dollar and adds Roth balance; a dollar used to harvest a long-term gain within the 0% band is taxed at 0% and resets cost basis higher, but adds no Roth balance. A gap-allocation framework typically runs in this order:
- Do the conversion first to absorb the standard deduction. In 2026 the standard deduction is $32,200 for married filing jointly and $16,100 for single filers, so the first conversion dollars fall against that deduction before any bracket applies.
- Project baseline taxable income before any conversion or harvest, including interest, dividends, pensions, and wages.
- Measure the gap between that baseline and the 0% capital gains ceiling ($98,900 for married filing jointly in 2026, per Rev. Proc. 2025-32).
- Value the alternatives: weigh converting at today’s ordinary rate against locking in a tax-free gain and a higher basis.
- Check the next-tier cost: every dollar of gap filled with conversion income pushes one dollar of gain into the 15% bracket, so count how many gain dollars would be repriced.
- Account for future years: required minimum distributions at age 73 (age 75 for those born in 1960 or later), a surviving-spouse filing change, and inheritance timelines all shift which option carries more long-run value.
The reverse direction is easy to miss: harvested gains are part of taxable income and MAGI too, so a large 0% harvest raises the totals used for the conversion’s own bracket, NIIT, and IRMAA math. Gap years and loss years shift the calculus; see a Roth conversion in a low-income year.
Can a conversion trigger the 3.8% Net Investment Income Tax on my gains?
A Roth conversion is not itself net investment income, because IRA and qualified-plan distributions are excluded from the 3.8% Net Investment Income Tax (Source: IRS Net Investment Income Tax Q&A). The conversion cannot be taxed by NIIT directly. It can still cause NIIT indirectly by raising modified adjusted gross income.
NIIT applies 3.8% to the lesser of net investment income or the amount by which MAGI exceeds a fixed threshold: $250,000 for married filing jointly, $200,000 for single and head of household, and $125,000 for married filing separately (Source: IRS Topic No. 559). These thresholds are statutory and are not indexed for inflation.
Because a conversion increases MAGI, it can lift MAGI above the threshold and expose your other net investment income, such as capital gains and dividends, to the 3.8% tax even though the conversion dollars themselves are exempt. For the mechanics, see the Q3 Advisors overview of the Net Investment Income Tax for 2026.
Medicare IRMAA: how a conversion today raises premiums two years later
A Roth conversion raises MAGI, and Medicare uses MAGI to set income-related monthly adjustment amounts (IRMAA) for Part B and Part D. Because IRMAA uses a two-year lookback, a conversion completed in 2026 can raise premiums in 2028 (Source: SSA POMS HI 01101.020). The standard 2026 Part B premium is $202.90 per month (Source: medicare.gov Publication 11579), and IRMAA surcharges begin above $109,000 MAGI for single filers and $218,000 for joint filers.
| 2026 MAGI, single | 2026 MAGI, married filing jointly | Part B monthly | Part D add-on |
|---|---|---|---|
| ≤ $109,000 | ≤ $218,000 | $202.90 (standard) | $0.00 |
| > $109,000 to $137,000 | > $218,000 to $274,000 | $284.10 | +$14.50 |
| > $137,000 to $171,000 | > $274,000 to $342,000 | $405.80 | +$37.50 |
| > $171,000 to $205,000 | > $342,000 to $410,000 | $527.50 | +$60.40 |
| > $205,000 to < $500,000 | > $410,000 to < $750,000 | $649.20 | +$83.30 |
| ≥ $500,000 | ≥ $750,000 | $689.90 | +$91.00 |
Sources: SSA POMS HI 01101.020 (2026 IRMAA tiers); medicare.gov Pub 11579 (standard 2026 Part B premium). 2026 tiers use 2024 MAGI, or 2023 if 2024 is unavailable.
The interaction with capital gains is direct: gains you harvest in the same year as a conversion also raise MAGI, so a coordinated year can cross an IRMAA tier that either move alone would not. Because of the two-year lookback, the last conversion year that does not affect a future premium is age 62.
A worked example of the stacking order
Consider a married-filing-jointly household in 2026 with $60,000 of taxable income before any gains or conversion, planning around the $98,900 zero-rate ceiling (Source: Rev. Proc. 2025-32). The table shows how the same $30,000 long-term gain is taxed differently depending on whether a $30,000 conversion is stacked underneath it.
| Scenario (2026 MFJ) | Ordinary income | Long-term gain | 0% gain room used | Gain taxed at 15% |
|---|---|---|---|---|
| No conversion | $60,000 | $30,000 | $30,000 (all fits under $98,900) | $0 |
| $30,000 conversion added | $90,000 | $30,000 | $8,900 | $21,100 |
Illustration using 2026 breakpoints from Rev. Proc. 2025-32; figures are hypothetical and for education only.
In the first row the full $30,000 gain fits beneath the ceiling and is taxed at 0%. In the second row the conversion raises ordinary income to $90,000, leaving only $8,900 of room, so $21,100 of the same gain is taxed at 15%. The gain never changed; the ordinary income stacked beneath it did.
How do Roth assets change the future picture?
Qualified withdrawals from a Roth IRA are not counted in taxable income or MAGI, so in later years Roth balances can help keep taxable income beneath the 0% capital gains ceiling and below the NIIT and IRMAA thresholds. That is one reason the timing of a Roth conversion is often weighed against its bracket, NIIT, and IRMAA cost in the conversion year (Source: IRS Pub 590-B). This is education, not a recommendation.
Work with Q3 Advisors
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
Does a Roth conversion count as a capital gain?
No. A Roth conversion is ordinary income, not a capital gain, and it is reported on Form 8606 to Form 1040 line 4b (Source: IRS Pub 590-B). It is taxed in the ordinary-income brackets and never qualifies for the 0%, 15%, or 20% preferential long-term capital gains rates that apply to gains and qualified dividends.
Can a Roth conversion push my capital gains into a higher tax bracket?
Yes. Ordinary income, including a conversion, stacks first, and long-term gains are measured on top of it (Source: IRS Topic No. 409). By raising taxable income, a conversion can push gains that would have been taxed at 0% into the 15% band, or from 15% toward 20%, once income crosses the relevant 2026 breakpoint (Source: Rev. Proc. 2025-32).
Should I harvest capital gains at 0% or do a Roth conversion?
The rules allow either, but both draw on the same bracket room beneath the 0% ceiling, so in a low-income year a household often cannot maximize both (Source: IRS Topic No. 409; Rev. Proc. 2025-32). One approach is to compare the ordinary-rate cost of converting against the value of a tax-free gain and a higher basis. The right balance depends on individual circumstances.
Do capital gains count as income for a Roth conversion?
Long-term gains and qualified dividends are part of taxable income and MAGI, so harvesting gains in a conversion year raises the totals used for capital gains breakpoints, NIIT thresholds, and Medicare IRMAA tiers (Sources: IRS Topic No. 409; SSA POMS HI 01101.020). Gains do not change the fact that a conversion is fully allowed, but they can raise its bracket, NIIT, and IRMAA cost.
Is a Roth conversion subject to the Net Investment Income Tax?
The conversion itself is not, because IRA and qualified-plan distributions are excluded from net investment income (Source: IRS NIIT Q&A). However, a conversion raises MAGI, and if MAGI crosses the fixed threshold, $250,000 for married filing jointly or $200,000 for single filers, your other investment income such as capital gains may become subject to the 3.8% tax.
Is there an income limit for a Roth conversion?
No. The pre-2010 $100,000 MAGI limit on conversions was permanently repealed, so a Roth conversion is available at any income level (Source: IRS Pub 590-A). Roth contributions still face income phase-outs, but conversions do not. Higher income does raise the odds that conversion income interacts with the 15% or 20% gains bands, NIIT, and IRMAA.
Sources
IRS Topic No. 409, Capital Gains and Losses: https://www.irs.gov/taxtopics/tc409
IRS Rev. Proc. 2025-32 (2026 capital gains rate amounts): https://www.irs.gov/pub/irs-drop/rp-25-32.pdf
IRS Rev. Proc. 2024-40 (2025 amounts): https://www.irs.gov/pub/irs-drop/rp-24-40.pdf
IRS Publication 590-A, Contributions to IRAs: https://www.irs.gov/publications/p590a
IRS Publication 590-B, Distributions from IRAs: https://www.irs.gov/publications/p590b
IRS Instructions for Form 8606: https://www.irs.gov/instructions/i8606
IRS Questions and Answers on the Net Investment Income Tax: https://www.irs.gov/newsroom/questions-and-answers-on-the-net-investment-income-tax
IRS Topic No. 559, Net Investment Income Tax: https://www.irs.gov/taxtopics/tc559
SSA POMS HI 01101.020 (2026 IRMAA tiers): https://secure.ssa.gov/poms.nsf/lnx/0601101020
medicare.gov Publication 11579 (2026 Medicare costs): https://www.medicare.gov/publications/11579-medicare-costs.pdf
