Roth Conversion Strategy: When and How Much to Convert in Retirement

A Roth conversion is the most powerful tax-planning move available to a retiree with substantial pre-tax savings. By moving money from a traditional IRA or 401(k) into a Roth account, you pay income tax now in exchange for tax-free growth and tax-free withdrawals forever after. Done well — usually during the "gap years" between retirement and Required Minimum Distributions — a multi-year conversion ladder can save a household six figures in lifetime tax. Done poorly, it can push you into a higher bracket, trigger Medicare surcharges, and disqualify you from Affordable Care Act subsidies.

The strategy is not for everyone. It works best for households with a large pre-tax balance, a long time horizon, and a window of years where taxable income is unusually low. Households already in the top tax bracket, or those who expect to be in a lower bracket in retirement, may find that deferring tax is still the better play. This guide covers the mechanics, the timing, and the cliffs that catch unwary converters.

What a Roth conversion actually does

A Roth conversion moves money from a traditional pre-tax account — typically a traditional IRA, but sometimes a traditional 401(k) — into a Roth account. The amount converted is added to your ordinary income for the year and taxed at your marginal rate. Once in the Roth, the money grows tax-free and qualified withdrawals are tax-free. There is no income limit on who can convert — anyone with a traditional IRA can do it, regardless of how high their income is. This is what makes the "backdoor Roth" strategy possible for high earners.

The conversion itself does not require selling investments. You can convert shares of a mutual fund or ETF directly, in-kind, from the traditional IRA to the Roth IRA. The IRS treats this as a taxable event based on the value of the assets on the date of conversion, but the investments themselves continue uninterrupted. You owe tax on the conversion amount, which means you need to have cash available from a non-retirement source to pay the tax bill. Using part of the converted amount to pay the tax is a costly mistake — it reduces the Roth balance and, if you are under 59½, may trigger a 10% early withdrawal penalty on the amount used to pay tax.

The gap years: when conversions shine

The best time to do Roth conversions is during the "gap years" — the period between retirement and the start of Social Security and Required Minimum Distributions. During these years, taxable income often drops dramatically. The retiree is no longer earning a salary, has not yet started Social Security, and is not yet required to take RMDs. This creates a window where large amounts can be converted at low marginal rates — often 12% or 22%, instead of the 24% or 32% the household paid during working years.

Consider a couple retiring at 60 with $1.5 million in traditional IRAs. They plan to delay Social Security to age 70 and will start RMDs at 73. They have roughly 13 years (60 to 73) of low-income gap years. Converting $100,000 per year during this window, if it can be done within the 22% bracket, moves $1.3 million into Roth status at a known, low tax rate. Without these conversions, the same money would be forced out as RMDs starting at 73, layered on top of Social Security, and likely taxed at 24% or higher.

Filling the bracket without spilling over

The core technique of a Roth conversion is "filling the bracket." You convert an amount that brings your taxable income up to the top of a favorable tax bracket — usually the 22% or 24% federal bracket — without crossing into the next one. The 2025 brackets for married filing jointly, for example, have the 22% bracket topping out at $394,600 of taxable income, and the 24% bracket topping out at $467,650. A couple with $80,000 of other income could convert up to roughly $314,600 at the 22% rate before spilling into the 24% bracket.

State income tax also matters. Residents of states with no income tax — Florida, Texas, Washington, Nevada, Wyoming, South Dakota, Alaska, and (effectively) Tennessee — face only the federal bill. Residents of high-tax states like California (top rate 13.3%) or New York (top rate 10.9%) need to factor state tax into the conversion calculation, and may find conversions less attractive unless they plan to relocate. Some retirees move to a no-tax state, do their conversions there, and then move back — a strategy that works but requires establishing genuine residency to avoid audit.

The ACA premium tax credit cliff

For retirees under 65 who buy health insurance through the Affordable Care Act marketplace, Roth conversions can trigger a steep subsidy cliff. The ACA premium tax credit phases out as modified adjusted gross income rises, and above 400% of the federal poverty level (about $60,000 for a single filer or $80,000 for a couple in 2025), the credit disappears entirely. A conversion that pushes MAGI from $59,000 to $80,000 can wipe out thousands of dollars in premium subsidies.

The math is unforgiving. A retiree receiving $700 per month in ACA subsidies loses $8,400 per year if a conversion pushes them over the cliff. If they convert $30,000 in that year, the $8,400 subsidy loss is effectively a 28% surcharge on top of the federal income tax. For ACA-eligible retirees, the strategy is to keep MAGI just below the cliff in subsidy years and convert more aggressively in the year they turn 65 and transition to Medicare.

The IRMAA Medicare cliff

For retirees 65 and over on Medicare, the equivalent cliff is IRMAA — the Income-Related Monthly Adjustment Amount. IRMAA adds surcharges to Medicare Part B and Part D premiums based on modified adjusted gross income from two years prior. The 2025 IRMAA tiers begin at $106,000 MAGI for single filers and $212,000 for joint filers, with surcharges escalating at five income brackets above those thresholds. Crossing a tier boundary by even $1 can cost hundreds of dollars per month in additional premiums.

Because IRMAA looks back two years, a conversion done at age 63 affects Medicare premiums at age 65. The 2025 Part B standard premium is $185.00 per month; the top IRMAA tier adds another $506.90 per month, or $6,083 per year. A retiree considering a large conversion should map out the IRMAA impact across multiple years, sometimes splitting a large conversion across two tax years to stay within a lower tier. The Form SSA-44 life-changing event appeal — for retirement, work reduction, or death of a spouse — can reset IRMAA mid-cycle, but only for specific qualifying events.

The pro-rata rule trap

The pro-rata rule is the single most overlooked Roth conversion trap. When you convert any amount from a traditional IRA, the IRS treats all of your traditional IRA balances as a single pool, and the conversion is treated as coming proportionally from the pre-tax and after-tax portions of that pool. If you have $90,000 in pre-tax traditional IRA funds and $10,000 in after-tax basis (from non-deductible contributions), and you convert $10,000, only $1,000 of the conversion is tax-free — the rest is taxable.

The pro-rata rule makes the "backdoor Roth" strategy — contributing to a non-deductible traditional IRA and immediately converting — much less attractive for anyone who already has a substantial pre-tax traditional IRA balance. The fix is to roll the pre-tax traditional IRA into an employer 401(k) plan first, leaving only the after-tax basis in the traditional IRA. Then a conversion of that basis is mostly tax-free. This requires an employer plan that accepts incoming rollovers, and not all do.

The 5-year rule on conversions

Each Roth conversion has its own 5-year clock for penalty-free withdrawal of principal. If you convert at age 55 and want to withdraw the converted amount at age 58, the withdrawal is penalty-free even though you are under 59½ — because the 5-year clock on that conversion has expired. But if you convert at age 55 and withdraw at age 57, the withdrawal is hit with a 10% early withdrawal penalty on the converted amount (no tax, since you already paid tax on conversion).

The rule is per-conversion, not per-account, which means tracking matters if you do conversions across multiple years. The ordering rules for Roth withdrawals help: contributions come out first (always tax and penalty free), then conversions (in chronological order, each with its own 5-year clock), then earnings (tax and penalty free only after age 59½ and the account's 5-year clock). For most retirees, the 5-year rule on conversions is a non-issue because they are converting for long-term tax savings, not for short-term withdrawals — but it is the kind of detail that catches people who plan to use Roth conversions as an early-retirement income source.

Frequently asked questions

---

Last reviewed June 28, 2026. This article is informational and does not constitute legal, tax, or financial advice. Consult a qualified professional for guidance specific to your situation.