Part 1 — Direct Answer

The optimal time for Roth conversions is the window between retirement and age 73 — when your earned income has stopped or dropped significantly, Social Security may still be deferred, and Required Minimum Distributions haven't started yet. This period often represents the lowest taxable income years of your entire retirement, creating an opportunity to convert pre-tax IRA dollars to Roth at the lowest available tax rates. Once RMDs begin at 73, your taxable income floor rises and the conversion window narrows significantly.

Part 2 — Detailed Explanation

Roth conversions are a tax arbitrage strategy. You pay income tax on the converted amount today in exchange for permanently tax-free growth and withdrawals in the future. The logic only works in your favor if the tax rate you pay today is lower than the rate you would have paid on those same dollars in the future. Identifying your conversion window means identifying the years where that trade-off is most favorable.

For most pre-retirees with significant pre-tax account balances, the favorable window opens when employment income stops and closes when RMDs begin. Consider the income trajectory: during your working years, your income is typically at its highest, making conversions expensive. The year you retire, your income often drops dramatically. If you defer Social Security and haven't yet hit the RMD age, you may have five to fifteen years of relatively low taxable income — years where you can convert IRA assets at the 12% or 22% federal bracket rather than the 32% or higher bracket you might face once RMDs and Social Security combine.

The conversion amount each year should be calibrated to fill your current tax bracket without spilling into the next one — or into IRMAA Medicare surcharge territory two years later. For a married couple filing jointly in 2026, the 22% bracket extends to approximately $201,050 in taxable income. If your baseline retirement income — Social Security deferred, no RMDs yet — is $80,000, you have roughly $120,000 of bracket space available for Roth conversions before hitting the 24% bracket. Converting that amount each year for ten years can dramatically reduce the pre-tax balance that will eventually generate forced RMDs.

The conversion decision also interacts with Social Security timing. Many retirees who delay Social Security to age 70 for the maximum benefit find themselves with a gap period — typically ages 62-70 — where income is low but living expenses continue. This gap period is often the single best conversion window available. Using IRA assets to fund living expenses during this gap while also converting additional amounts into Roth can be highly efficient from a lifetime tax standpoint.

Arizona residents have an additional reason to convert aggressively during lower-income years: Arizona does not tax Roth IRA withdrawals. Every dollar converted and placed in Roth is permanently exempt from both federal income tax and Arizona state income tax on future distributions — at Arizona's flat 2.5% rate, the savings compound meaningfully over a 20-30 year retirement.

Part 3 — What This Means for You

If you are 58-65 and planning to retire in the next few years, the time to start modeling your conversion strategy is before you retire — not after. The first year of retirement is often the best conversion year of your life. Your earned income drops, your bracket drops, and you have maximum runway before RMDs force distributions at potentially higher rates.

The mistake most pre-retirees make is waiting until they're settled into retirement to think about Roth conversions. By then, they've often already missed one or two prime conversion years. A proper conversion plan should be built during the last two to three years of employment, so it is ready to execute the moment your W-2 income stops.

For a household with $2M in a traditional IRA and $500K in a Roth IRA, a disciplined ten-year conversion strategy starting at retirement can shift hundreds of thousands of dollars into Roth — permanently reducing future RMDs, permanently reducing IRMAA exposure, and permanently improving the tax position of the surviving spouse who will eventually file as a single taxpayer at compressed brackets.

Part 4 — Common Mistakes and Misconceptions

• The most common mistake is converting too much in a single year. Taking a large IRA distribution to fund a conversion without modeling the tax bracket impact often results in paying 32% or 35% on the top dollars when 22% or 24% was available with a smaller, multi-year approach.
• The second mistake is ignoring IRMAA. A $200,000 conversion in 2026 might seem cost-effective from a bracket standpoint but could trigger a significant IRMAA surcharge in 2028. Modeling both tax brackets and IRMAA simultaneously is essential.
• The third mistake is converting too little. Some retirees do a token $20,000-$30,000 conversion and feel like they've checked the box. For someone with $2M+ in pre-tax accounts, that pace barely moves the needle on lifetime tax exposure.