Roth Conversion Timing: When Converting Makes Sense and When It Doesn't

Why Roth Conversions Matter

The core question behind every Roth conversion is simple: would you rather pay taxes now or later? A traditional IRA or 401(k) gives you a tax deduction when you contribute, but every dollar withdrawn in retirement is taxed as ordinary income. A Roth IRA offers no upfront deduction, but qualified withdrawals — including all growth — are completely tax-free.

A Roth conversion bridges the two. You move money from a traditional account to a Roth, pay income tax on the converted amount today, and then enjoy tax-free growth and withdrawals for the rest of your life. The strategy makes sense when you can pay a lower tax rate on the conversion now than you would pay on withdrawals later. The challenge is predicting future tax rates — a task that requires understanding your income trajectory, Social Security timing, RMD obligations, and the political landscape of tax policy.

Beyond the rate comparison, Roth conversions provide three additional benefits. First, Roth IRAs have no Required Minimum Distributions during the owner's lifetime, giving you more control over retirement income and tax planning. Second, Roth IRAs provide tax-free inheritance for beneficiaries — increasingly valuable since the SECURE Act imposed a 10-year distribution requirement on inherited retirement accounts. Third, tax diversification — having both traditional and Roth accounts — gives you flexibility to manage taxable income year by year in retirement.

The Conversion Window: Early Retirement Years

The most powerful conversion window for most people is the gap between retirement (or career downshift) and the start of Social Security and RMDs. During these years — often age 60 to 72 — your taxable income may be significantly lower than during your working years or later retirement years.

Consider a couple who retires at 62 with $1.5 million in traditional IRAs, a paid-off home, and moderate expenses of $80,000 per year. Before Social Security begins at 67 and RMDs at 73, their taxable income is minimal. They can convert $50,000 to $80,000 per year from traditional to Roth, paying taxes in the 12 or 22 percent bracket — rates they will likely never see again once Social Security, RMDs, and potential future tax increases push them into higher brackets.

By the time RMDs begin at 73, a series of strategic conversions has reduced the traditional IRA balance significantly. Smaller traditional balances mean smaller RMDs, less taxable income, potentially lower Medicare premiums, and reduced taxation of Social Security benefits. The cumulative tax savings over a 25-year retirement can easily reach $50,000 to $150,000 for households with significant traditional retirement balances.

How Much to Convert Each Year

The optimal conversion amount fills your current tax bracket without pushing you into the next one. This requires knowing where your current bracket ends and how much room remains. In 2024, the 12 percent bracket for married filing jointly ended at $94,300 of taxable income. The 22 percent bracket ended at $201,050. The 24 percent bracket ended at $383,900.

If your taxable income without a conversion is $40,000 (from investment income and part-time work), and you want to stay in the 12 percent bracket, you could convert up to $54,300 ($94,300 minus $40,000). Alternatively, if you are comfortable paying 22 percent, you could convert up to $161,050 and fill the entire 22 percent bracket.

The decision depends on your expected future rate. If you believe your marginal rate in retirement will be 24 percent or higher (due to RMDs, Social Security, and potential tax increases), converting at 22 percent today saves money. If you believe your future rate will be 22 percent or lower, converting at 22 percent is neutral or slightly negative after accounting for the time value of money. The break-even analysis depends on your conversion tax rate, your expected withdrawal tax rate, the investment return, and the time horizon — a financial advisor or tax planning software can model your specific situation.

The Medicare IRMAA Trap

One of the most common mistakes in Roth conversion planning is ignoring the Income-Related Monthly Adjustment Amount (IRMAA). Medicare uses your modified adjusted gross income from two years prior to determine Part B and Part D premiums. A large Roth conversion at age 63 increases your MAGI for that year, which triggers higher Medicare premiums at age 65 — your first year of Medicare eligibility.

IRMAA surcharges are significant. In 2024, individuals with MAGI above $103,000 (or $206,000 for married couples) paid an additional $65.90 to $384.30 per month in Part B premiums, plus surcharges on Part D. For a couple, IRMAA surcharges can add $3,000 to $9,000 per year to Medicare costs — potentially offsetting the tax savings from the conversion.

The solution is awareness and planning. Map your conversion amounts against IRMAA thresholds. In some cases, it makes sense to convert slightly less to stay below an IRMAA tier. In other cases, the long-term tax savings from a larger conversion outweigh two years of higher Medicare premiums. Run the numbers for your specific situation — the optimal answer is usually not obvious.

Building a Multi-Year Conversion Plan

Roth conversions are not a one-time decision — they are a multi-year strategy. The most effective approach is to model conversions over a 5 to 15 year horizon, considering projected income, Social Security start dates, RMD schedules, tax bracket projections, and IRMAA thresholds.

Start with your end goal: what traditional IRA balance do you want when RMDs begin? For many retirees, the answer is "small enough that RMDs do not push me into a higher tax bracket." If you have $1.5 million in traditional accounts and expect Social Security of $40,000 per year, your RMD at 73 would be approximately $58,000 — pushing combined income to $98,000 before any other sources. Converting $500,000 to $700,000 over a decade of lower-income years could reduce the RMD to a more manageable level.

Work backward from this target to determine annual conversion amounts, then overlay tax brackets and IRMAA thresholds. The result is a year-by-year plan that maximizes low-bracket conversions and avoids costly surprises. Review and adjust the plan annually — tax brackets change, investment returns fluctuate, and life circumstances evolve. The plan is a living document, not a fixed commitment.

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