The best Roth conversion window is usually after work income drops and before RMDs begin at 73. Those years are often the lowest-tax years of your retirement, which makes conversions far more efficient. Once RMDs start, your taxable income floor rises and the window gets tighter quickly.

Why the Pre-RMD Years Are Usually Your Lowest Tax Window

A Roth conversion is tax arbitrage. You pay tax now so those dollars can grow and later come out tax free. The strategy only wins when today's conversion rate is lower than the rate you would likely pay later on those same dollars.

For many pre-retirees with large pre-tax balances, that favorable window opens when employment income ends and closes when RMDs begin. Working years are usually your highest-income years, so conversions are expensive there. After retirement, if Social Security is delayed and RMDs have not started, you may get five to fifteen lower-income years where 12% or 22% brackets are available instead of 32% or higher later.

Annual conversion size should fill the current bracket deliberately without spilling into the next one or creating avoidable IRMAA exposure two years later. In 2026, the married-filing-jointly 22% bracket extends to about $201,050 of taxable income. If baseline retirement income is about $80,000 before RMDs and with Social Security deferred, that leaves roughly $120,000 of room for conversions before 24% rates.

Social Security timing changes the equation. Households that delay benefits to age 70 often create an income gap from roughly ages 62 to 70, and that gap is frequently the strongest conversion period in the plan. Using IRA dollars for spending during that stretch while converting additional amounts can be highly efficient over a full retirement.

Arizona adds another benefit. Roth IRA withdrawals are not taxed by Arizona, so each dollar moved to Roth during lower-income years is permanently outside both federal tax and Arizona's 2.5% flat state income tax on future distributions.

If Retirement Is Near, Build the Conversion Plan Before Your Last Paycheck

If you are 58 to 65 and retirement is near, conversion planning should start before your final paycheck. The first retirement year is often one of the best conversion years you will ever get because earned income falls and runway before RMDs is still long.

Waiting until you feel settled in retirement usually costs one or two prime years. The better move is to build the conversion plan during your last two to three working years so execution starts as soon as W-2 income stops.

For a household with $2 million in traditional IRA assets and $500,000 already in Roth, a disciplined ten-year conversion plan can move hundreds of thousands more into Roth. That can reduce future RMD pressure, reduce IRMAA exposure, and improve the tax position of the surviving spouse who eventually files as single under compressed brackets.

Three Conversion Errors That Shrink the Long-Term Benefit

• Converting too much in one year. Big one-off conversions can push top dollars into 32% or 35% brackets when a multi-year plan could have kept much of that income in the 22% or 24% range.
• Ignoring IRMAA in the conversion model. A $200,000 conversion in 2026 may look fine in isolation but can still create meaningful Medicare surcharges in 2028.
• Converting too little to matter. Token $20,000-$30,000 annual conversions rarely change the long-term outcome for households with $2 million or more in pre-tax assets.