The scenario
You have $300,000 in a traditional IRA from years of nondeductible contributions (tracked on Form 8606) and pre-tax rollovers. Your income already puts you in the 32% or 35% federal bracket. You can't contribute to a Roth IRA directly. You're wondering: should you convert the entire IRA to a Roth now and pay a large tax bill, or leave it as traditional and pay taxes when you withdraw in retirement?
The answer depends on comparing your marginal tax rate today against your expected effective tax rate on withdrawals in retirement — and accounting for several second-order effects that can swing the decision by tens of thousands of dollars.
The basic framework: convert if your rate drops
The simplest rule: if your tax rate on the conversion today is lower than your tax rate on future withdrawals, converting saves money. If your rate today is higher, waiting saves money.
But "your tax rate in retirement" is not a single number. It depends on:
- How much you'll withdraw annually
- Social Security benefits (up to 85% taxable, increasing your effective rate)
- Required Minimum Distributions pushing you into higher brackets
- IRMAA surcharges on Medicare premiums
- State taxes (which may change if you relocate)
- Future tax law changes (unknown but relevant)
The high-income conversion penalty
Converting $300,000 while earning a $250,000 salary means the conversion stacks on top of your existing income. After the 2026 standard deduction ($16,100 single), that salary is roughly $233,900 of taxable income before the conversion. The $300,000 conversion then stacks on top. Using 2026 brackets (single):
| Income layer | Amount | Marginal rate |
|---|---|---|
| Taxable salary (after std. deduction) | $233,900 | Already taxed |
| Conversion fills rest of 32% bracket ($233,900 → $256,225) | $22,325 | 32% |
| Conversion fills 35% bracket ($256,226 → $533,900) | $277,675 | 35% |
The 35% bracket runs all the way to $640,600 (2026), and the stacked total income here is only $533,900 — so none of this conversion reaches the 37% bracket.
Federal tax on the $300,000 conversion:
- $22,325 × 32% = $7,144
- $277,675 × 35% = $97,186
- Total ≈ $104,330
Plus state taxes: in California, add roughly 9-12% on most of the conversion, or another $27,000-$33,000.
Total tax cost: $131,000-$137,000 to get $300,000 into a Roth.
That's an effective rate of about 44-46% on the conversion. For this to be worthwhile, you'd need to face rates above 44% on future traditional IRA withdrawals — possible but not typical for most retirees.
The partial conversion strategy
Instead of converting $300,000 at once, spread conversions across multiple years — and ideally across years with lower income.
Scenario: convert $50,000/year for 6 years while still working
At a $250,000 salary, each $50,000 conversion lands in the 32-35% brackets:
- Tax per conversion: roughly $16,000-$17,500
- Total tax over 6 years: roughly $99,000-$105,000
This is only marginally better than a lump-sum conversion because your salary already occupies the lower brackets. The real savings come from converting in low-income years, not just smaller slices.
Better scenario: convert after retiring but before SS and RMDs
If you retire at 60 and delay Social Security to 70, your only income is the conversion itself. Using 2026 single brackets and the $16,100 standard deduction:
| Conversion layer | Amount | Tax rate |
|---|---|---|
| Standard deduction ($0 → $16,100) | $16,100 | 0% |
| 10% bracket ($0 → $12,400 taxable) | $12,400 | 10% |
| 12% bracket ($12,401 → $50,400 taxable) | $38,000 | 12% |
| 22% bracket ($50,401 → $100,800 taxable, capped at conversion) | $33,500 | 22% |
Converting $100,000/year during early retirement (= $16,100 deduction + $83,900 taxable) costs roughly:
- $12,400 × 10% = $1,240
- $38,000 × 12% = $4,560
- $33,500 × 22% = $7,370
- Total ≈ $13,170 per year — an effective rate of about 13% versus 35%+ while working.
Over 3 years, you convert the full $300,000 at a total cost of roughly $39,500 instead of $104,330.
That's about $65,000 in tax savings from timing alone.
The RMD trap that makes conversion attractive
If you leave $300,000 in a traditional IRA and it grows at 7% annually, in 15 years it's worth roughly $828,000. At age 73 (when RMDs begin for those born 1951–1959; age 75 for those born 1960 or later), your first-year RMD is approximately $31,200 — on top of Social Security and any other income.
By age 80, the RMD on the grown balance could be $45,000-$55,000/year. Combined with Social Security ($35,000-$45,000/year) and any pension or other income, you could easily be in the 22-24% bracket in retirement — higher than the 13% rate you'd pay converting during the early retirement gap.
More importantly, RMDs can trigger:
- IRMAA surcharges: Medicare Part B and D premiums increase at income thresholds ($109,000 single / $218,000 MFJ in 2026). A single surcharge tier can add $1,000-$4,000/year to healthcare costs.
- Social Security taxation: combined income above $34,000 (single) means up to 85% of SS benefits are taxable, effectively increasing your marginal rate by 15-25%.
- ACA subsidy cliffs: if you retire before 65 and need marketplace insurance, MAGI from RMDs can reduce or eliminate premium subsidies worth $5,000-$15,000/year.
When to convert while earning a high income
Despite the high upfront cost, converting during high-income years makes sense if:
- You expect even higher rates in retirement: large pension + SS + RMDs on a growing IRA could exceed your current income. Unlikely for most people, but possible for dual-income government employees or those with large inherited IRAs.
- You have significant basis (Form 8606): if $100,000 of your $300,000 IRA is nondeductible basis, only $200,000 is taxable on conversion. The effective rate on the full transfer is lower.
- You're in a temporarily low bracket: between jobs, starting a business with year-one losses, or taking a sabbatical.
- Estate planning goals: Roth IRAs have no RMDs during the owner's lifetime and pass to beneficiaries who receive tax-free distributions. If your estate is large enough that heirs will be in high brackets, converting now (even at a high rate) can reduce the total tax paid across generations.
The break-even analysis
To determine if converting now is better than waiting, compare two scenarios over your expected lifetime:
Convert now at 35%: $300,000 - $105,000 tax = $195,000 in Roth, growing tax-free at 7% for 25 years = $1,058,000, all tax-free.
Keep as traditional: $300,000 growing at 7% for 25 years = $1,629,000, but withdrawals are taxed. At an effective 20% rate in retirement, the after-tax value is $1,303,000.
In this comparison, keeping the traditional IRA wins by $245,000 in after-tax value — because the retirement tax rate (20%) is much lower than the conversion rate (35%).
Important caveat about where the tax is paid. The break-even above assumes the $105,000 conversion tax comes out of the IRA itself, so only $195,000 actually lands in the Roth and grows. That's the pessimistic case. If you instead pay the tax from outside (taxable) funds — which is the recommended approach — the full $300,000 grows in the Roth tax-free. At 7% for 25 years that's about $1,628,000 entirely tax-free, versus $1,303,000 after-tax in the traditional scenario. Paid from outside funds, the conversion looks dramatically more favorable, because you've effectively moved more money into the tax-free wrapper. This is why "pay the tax from non-IRA funds" is the single most important rule of conversions.
Also: if the retirement tax rate climbs to 30% (due to RMDs, IRMAA, SS taxation stacking), the traditional IRA's after-tax value drops to $1,140,000 — and even the tax-from-IRA Roth wins.
The crossover point (when paying tax from the IRA) is when your retirement effective rate exceeds roughly 33-35% — matching your conversion rate. Paying the tax from outside funds pushes that crossover much lower.
The optimal path for most high earners
- Don't convert while working at peak income. The marginal rate is too high.
- Plan for a conversion window. The years between retirement and age 73 (when RMDs begin) are the sweet spot. Even 3-5 years of conversions in the 12-22% brackets can dramatically reduce lifetime taxes.
- Convert partially each year. Fill up to the top of the 22% or 24% bracket and stop. Don't spill into 32%.
- Pay the tax from non-IRA funds. Never withhold tax from the conversion amount itself — that reduces the Roth balance and counts as a taxable distribution. Paying from outside funds lets the full conversion grow tax-free.
- Watch the IRMAA and ACA cliffs. A conversion that pushes you $1 over an IRMAA threshold costs an extra $1,000+ in Medicare premiums.
The bottom line
For a high earner with a $300,000 traditional IRA, converting now at 32-35% is usually the wrong move. The optimal strategy is to wait for a lower-income period — ideally early retirement before Social Security and RMDs begin — and convert in the 10-24% brackets. The tax savings from timing can exceed $60,000 on a $300,000 conversion — and if you pay the tax from outside funds, the case for converting gets stronger still.