Roth Conversion vs. Capital Gain Harvesting (2026)

When you weigh roth conversion vs capital gain harvesting in a low-income year, the hard reality is that both moves draw from the same finite pool of low-bracket room. Ordinary conversion income stacks first and long-term gains stack on top, so filling the bracket with a conversion can push otherwise tax-free gains into the 15% band. Most retirees cannot fully use both levers in one year.

The One-Year Tradeoff: Why You Usually Cannot Do Both

In any single tax year you hold a finite band of low-bracket room. A Roth conversion adds ordinary income; harvesting adds realized long-term gains. Because gains stack on top of ordinary income under the Internal Revenue Code, every dollar of conversion pushes a dollar of would-be 0% gain toward the 15% rate. That mechanical stacking is why the two levers rarely fit together fully.

How the stacking order works: ordinary income fills brackets first, gains stack on top

The code taxes ordinary income (wages, pensions, IRA distributions, and Roth conversions) first, filling the 10%, 12%, and higher brackets from the bottom. Long-term capital gains and qualified dividends are then layered on top of that ordinary income to determine which capital gains rate applies. The 0% long-term gains rate applies only to gains that land below the 0% ceiling once ordinary income is already counted underneath them.

For 2026, the 0% long-term gains ceiling (measured in taxable income, after deductions) is $49,450 for single filers and $98,900 for married couples filing jointly. Above those figures the rate steps to 15%, and to 20% only above $545,500 single or $613,700 joint. A Roth conversion is ordinary income, so it sits in the stack beneath your gains.

Why a Roth conversion mechanically pushes gains out of the 0% band

Since conversion income counts underneath your gains, each conversion dollar raises the floor that your gains stack on. Suppose a married couple has $0 taxable ordinary income and $60,000 of long-term gains sitting entirely in the 0% band. Converting $50,000 makes taxable ordinary income $50,000; now only $48,900 of gain ($98,900 minus $50,000) remains at 0%, and the rest is bumped to 15%. The conversion did not raise the ceiling. It ate the room beneath it.

The no-toggling constraint: you cannot fully convert and fully harvest in the same window

Because both moves consume the same space below the 0% ceiling, they are largely mutually exclusive within one tax year. You can convert, or harvest at 0%, or split the room between them, but you cannot max both. This is the sequencing question competitors often skip: not “what is a Roth conversion,” but “which lever should fill this year’s bracket room.” Deciding how much to convert to Roth is really the same act as deciding how much 0% harvesting room to give up.

Why Many Households Convert First in a Deep Low-Income Year

When a retiree faces meaningful future required minimum distributions, a conversion in a low-income year is often the default lever many households reach for. Converting at 10% or 12% today can replace ordinary income that would otherwise land at 22% to 32% once RMDs and Social Security begin. The larger the traditional balance and the longer the runway, the wider the potential gap a conversion can capture.

The tax-arbitrage math: a low-bracket conversion versus future RMD-era rates

The value of a conversion is the spread between today’s rate and the rate you would otherwise pay later. Converting at 12% now instead of paying 24% on a future RMD saves roughly 12 percentage points, about $1,200 per $10,000 converted; against a future 32% rate the spread is near 20 points, roughly $2,000 per $10,000. These are illustrative figures that ignore growth; tax-free compounding inside the Roth typically adds further value. The Roth conversion break-even analysis covers the mechanics.

When large future RMDs make conversion the clear case

RMDs begin at age 73, and the first-year Uniform Lifetime Table divisor of 26.5 means the first distribution is roughly 3.8% of the prior year-end balance. A $1,000,000 traditional IRA generates a first RMD near $37,700; a $2,000,000 balance, near $75,500. When projected RMDs plus Social Security and other income are likely to exceed the 0% gains ceiling or push into the 22% bracket, conversion generally has the stronger claim on the room. Projected required minimum distributions for 2026 help gauge that pressure.

The short-window case: why some accelerate conversions before Social Security and RMDs start

The years between retirement and the start of Social Security and RMDs are frequently the lowest-income window a retiree will ever see. Many investors treat this gap as a limited runway to convert at low rates. A Roth conversion ladder spreads the work across several such years so no single year is forced into a high bracket. Once benefits and distributions switch on, that low-bracket room narrows sharply.

When Harvesting 0% Gains Wins Instead

Harvesting is the comparison move, not a pivot away from retirement-tax planning. It can be a suitable use of the room when future RMDs are modest and the priority is resetting cost basis at no tax. Because the 0% gains rate versus a future 15% rate is a 15-point spread, harvesting inside the 0% band can, dollar for dollar, carry a wider rate arbitrage than a conversion filling the 12% bracket.

The 15% arbitrage: harvesting inside the 0% band

Filling the 12% ordinary bracket with a conversion captures roughly a 10-point spread over a future 22% rate. Harvesting a gain at 0% and repurchasing to reset basis captures a 15-point spread over a future 15% rate. On a pure rate-arbitrage basis, the harvest is wider. The catch is that the harvest only resets basis on existing gains; a conversion moves dollars into an account where future growth is never taxed again, which can outweigh the narrower spread.

Small projected RMDs and step-up-eligible portfolios favor harvesting

If projected RMDs are small (a modest traditional balance) the future ordinary rate you are trying to avoid may already be low, shrinking the conversion’s arbitrage. Meanwhile a large taxable brokerage account with embedded gains offers real 0% harvesting value, especially to diversify a concentrated position. In that profile many investors lean toward harvesting, subject to the step-up considerations discussed below.

The Social Security and IRMAA interactions

A common misconception is that harvesting sidesteps income thresholds that conversions trip. In reality, both realized gains and conversion income raise provisional income for Social Security taxation and MAGI for IRMAA, so both can trigger those costs. The honest framing is not which move avoids the thresholds, but which buys more long-run value per dollar of that shared cost. Conversion income can also interact with the 3.8% net investment income tax by raising MAGI, though a conversion is not itself net investment income.

The Hybrid Approach: Splitting the Room Between Both

Because the 0% gains ceiling ($98,900 joint) sits just below the top of the 12% ordinary bracket ($100,800 joint), a common approach is to split the shared room deliberately: converting part of it at 10% to 12%, harvesting the remainder at 0%, then optionally converting the small sliver above the gains ceiling that gains cannot reach at 0% anyway. The right split depends on RMD size, time horizon, and legacy goals.

Worked example: splitting the bracket between conversion and 0% harvest

An illustrative married couple, both 66 and retired, sit in 2026 before Social Security and RMDs. With a base standard deduction of $32,200 plus the age-65 additional amount ($1,650 per spouse), and $10,000 of other ordinary income, most of that income is absorbed by deductions. This hypothetical is for education only and is not a projected result.

The couple both converts and harvests, but neither is maxed: the $70,000 conversion and the $54,400 harvest together consume one shared pool of room.

A year-by-year decision checklist

One approach many planners weigh, year by year:

• Size of projected RMDs and the traditional balance driving them.
• Years of low-income runway before Social Security and RMDs begin.
• Social Security claiming timing and provisional-income headroom.
• IRMAA MAGI position and any two-year lookback consequences.
• Whether appreciated assets are likely to be held until death (step-up) or sold sooner.
• How much of this year’s bracket room a conversion versus a harvest would use.

Sequencing across multiple low-income years, not just one

The single-year tradeoff eases when you plan a multi-year window. Some years may tilt toward conversion, others toward harvesting, as balances, income, and thresholds shift. Meeting the annual Roth conversion deadline of December 31 matters because a conversion is irreversible and cannot be undone in a later year. Modeling the full window, rather than optimizing one year in isolation, is where much of the value tends to sit.

Frequently asked questions

How much long-term gain can I harvest tax-free in 2026?

In 2026 the 0% long-term gains ceiling is $49,450 of taxable income for single filers and $98,900 for married couples filing jointly. Other ordinary income fills that space first. The table below shows the approximate tax-free gain room at $0 and $30,000 of other taxable income (income already net of the standard deduction).

Adding the standard deduction back ($16,100 single, $32,200 joint) raises the gross income that still qualifies.

If I convert $50,000 while sitting on $47,000 of gains, how much gets bumped to 15%?

It depends on your other income. In an illustrative case with $30,000 of other taxable income (joint), pre-conversion the $47,000 of gains fits inside the 0% band. A $50,000 conversion raises taxable ordinary income to $80,000, leaving only $18,900 of 0% room; the remaining $28,100 of gain is bumped to 15%, a tax cost near $4,215. This hypothetical is for education only.

Is the conversion arbitrage or the harvesting arbitrage bigger?

On a rate-spread basis, harvesting can be wider. Filling the 12% ordinary bracket with a conversion captures about a 10-point spread over a future 22% rate, while harvesting at 0% versus a future 15% rate is a 15-point spread. A conversion, however, shelters all future growth from tax, which can outweigh the narrower spread over a long horizon.

How much does converting at 12% now instead of 24% to 32% later save per $10,000?

The saving equals the rate spread. Converting at 12% instead of a future 24% rate saves about 12 percentage points, roughly $1,200 per $10,000 converted. Against a future 32% rate the spread is near 20 points, roughly $2,000 per $10,000. These illustrative figures ignore growth; tax-free compounding inside the Roth typically increases the long-run advantage.

What size traditional IRA balance tips the decision toward conversion?

There is no single number, but RMD pressure is the trigger. Because the first RMD at 73 is roughly 3.8% of the prior year-end balance, a $1,000,000 balance produces a first RMD near $37,700 and a $2,000,000 balance near $75,500. When projected RMDs plus Social Security and other income are likely to exceed the 0% gains ceiling or reach the 22% bracket, conversion generally has the stronger case.

Does harvesting gains avoid the Social Security torpedo or IRMAA?

Not reliably. Both realized long-term gains and conversion income raise provisional income for Social Security taxation (first tier $25,000 single, $32,000 joint; second tier $34,000 and $44,000) and MAGI for IRMAA. In the phase-in range, each added dollar can make $0.50 then $0.85 of benefits taxable. Neither move is a clean way around these thresholds.

What are the 2026 IRMAA thresholds and first-tier cost?

The 2026 first IRMAA tier begins at MAGI above $109,000 single or $218,000 joint, using a two-year lookback. Crossing it adds about $81.20 per month to Medicare Part B (roughly $974 per year per person, on top of the $202.90 standard premium), plus a Part D surcharge. IRMAA is a cliff: exceeding a threshold by $1 triggers the full tier, and it applies per person.

How do these moves affect ACA premium tax credits before age 65?

For early retirees under 65 buying marketplace coverage, both conversion income and realized capital gains raise ACA MAGI dollar for dollar and reduce premium tax credits on the same basis. Neither move is advantaged for subsidy purposes; the credit reduction depends on where you sit on the applicable-percentage curve. Coordinating conversions or harvesting with ACA eligibility is often a year-by-year balancing act.

What about the step-up in basis for heirs?

Assets held until death generally receive a basis step-up to fair market value, erasing the embedded gain for heirs. Harvesting a gain you would otherwise have held to death forfeits that free step-up, so if the harvest triggers any positive tax (a 15% spillover, or Social Security or IRMAA cost), that tax is pure cost. Harvesting adds value mainly when it resets basis on gains you will realize before death or reduces concentration risk.