There is a 12-year window in most retirees' lives — roughly age 60 to age 72 — where federal taxable income drops dramatically. Wages have stopped. Social Security hasn't started, or it's just starting. Required Minimum Distributions (RMDs) from Traditional IRAs and 401(k)s don't kick in until age 73 (or 75 for those born 1960+). For these years, your taxable income can be tens of thousands of dollars lower than it was in your peak earning years — and lower than it will be once RMDs force money out of pre-tax accounts at age 73. This window is the single biggest tax-planning opportunity in a retiree's life. Most people waste it.
Here's why the window matters. A typical 60-year-old with $1.2M in a Traditional 401(k) faces a math problem. That balance, growing at 6% per year, becomes roughly $1.8M by age 73 when RMDs begin. The first-year RMD divisor at age 73 is 26.5, so the forced distribution is about $68,000. Add Social Security of ~$36,000/year and you're at $104,000 in gross income before any pension, dividend, or part-time wage income. That's solidly in the 22% bracket — and the divisor drops every year, pushing RMDs into the 24% and eventually 32% brackets by your late 80s. If you took zero RMDs (because the accounts grew too large), you'd be in a much higher bracket than necessary for the rest of your life.
Roth conversions fix this. A Roth conversion moves money from a Traditional IRA to a Roth IRA. You pay ordinary income tax on the converted amount in the year of conversion. The money then grows tax-free, comes out tax-free, and has no RMD requirement during your lifetime. The strategic move is to convert during low-income years — exactly the 60-72 window — to fill up the lower federal tax brackets at favorable rates, then enjoy lower RMD-driven income later.
Let's run the numbers. Same retiree, age 60, $1.2M Traditional IRA, $40,000 of other income (small pension + part-time work). The 12% federal bracket tops at $99,700 for married filers in 2026. That means there's $59,700 of 'room' in the 12% bracket — you could convert $59,700 to Roth this year and pay only 12% federal tax on it. Do that every year from age 60 through age 72 and you've converted roughly $716,000 to Roth at an average 12% federal rate. The remaining Traditional IRA balance at age 73 might be $400,000-$600,000 instead of $1.8M, which dramatically reduces lifetime RMDs.
The IRMAA threshold is the next layer to understand. Medicare Income-Related Monthly Adjustment Amounts (IRMAA) kick in once you're on Medicare and modify your Part B and Part D premiums based on your tax return from two years prior. In 2026, the first IRMAA tier hits at $212,000 MAGI for married filers, adding about $84/month per person to Part B premiums. Higher tiers add hundreds more. If your Roth conversion strategy pushes you over an IRMAA tier, the surcharge can eat into the conversion savings. Conversions executed before age 63 (since the two-year lookback won't affect your first Medicare year at 65) escape IRMAA entirely.
Social Security taxation is the other landmine. Up to 85% of Social Security benefits become taxable once 'provisional income' (other income + 0.5 × benefits + tax-exempt interest) exceeds $44,000 for married filers. A Roth conversion increases provisional income, which can suddenly make a chunk of your Social Security benefits taxable that wasn't before. The combined marginal rate during this 'tax torpedo' zone can hit 40.7% (22% federal × 1.85, since each conversion dollar also exposes $0.85 of SS to taxation). Many advisors recommend doing conversions before claiming Social Security to avoid this entirely.
Net Investment Income Tax (NIIT) is the third consideration. The 3.8% NIIT applies to investment income (capital gains, dividends, interest) when MAGI exceeds $250,000 for married filers. Roth conversions raise your MAGI for that year, potentially pushing investment income above the NIIT threshold. For high-net-worth retirees with significant taxable account income, planning conversions to stay under the NIIT line during years with large capital gains can save meaningful tax.
The size of the optimal conversion depends entirely on bracket math. If you're a married filer with $60,000 of other income, the 22% bracket tops at $212,900 in taxable income (so roughly $245,000 gross), giving you $185,000 of room. Filling that bracket means converting $185,000 at an average federal rate of about 18%. The 24% bracket extends to $406,550, opening up another $193,000 of room at 24%. Above 24%, the math turns less favorable — most retirees will be in the 12% or 22% bracket in their RMD years, so converting at 32% or higher rarely pays off.
Timing within the window matters. Many retirees should front-load conversions in years 1-5 of retirement (age 60-65) for two reasons. First, you're not on Medicare yet, so IRMAA doesn't apply. Second, the conversion compounds inside the Roth for the longest possible time. A dollar converted at age 60 has 25-30 years to grow tax-free; a dollar converted at age 71 has maybe 15 years. The longer the tax-free growth runway, the larger the eventual benefit relative to the upfront tax cost.
Spouse death changes the calculus dramatically. When one spouse dies, the survivor immediately drops from Married Filing Jointly brackets to Single brackets — and Single brackets compress hard. The 22% bracket that tops at $212,900 for MFJ tops at just $106,450 for Single. RMDs continuing into widowed status can push income into much higher brackets than would have applied jointly. This is why widowed retirees often face brutal tax surprises in their first solo year. Pre-conversion during the joint years protects against this asymmetry.
Estate planning amplifies the case for Roth conversions. Heirs who inherit Traditional IRAs are usually subject to the SECURE Act 10-year rule — they must empty the account by year 10, paying ordinary income tax at their own marginal rate during their peak earning years. A 45-year-old neurosurgeon inheriting Dad's $800,000 Traditional IRA will pay federal tax on the distributions at 32-35%. Inheriting that same $800,000 in a Roth IRA means tax-free distributions. Converting in your 60s at 22% to spare your heirs from paying 32-35% later is one of the highest-leverage moves in personal finance.
When NOT to convert: if you expect your retirement-year tax bracket to be lower than your current bracket (rare but possible for very high earners who retire and stop working entirely), conversions don't pay off. If you have charitable intentions, leaving Traditional IRA assets and using Qualified Charitable Distributions (QCDs) after age 70½ lets you give pre-tax money to charity, which is strictly better than converting first. If you have a state income tax now but plan to move to a no-tax state, delaying conversions until after the move saves the state tax bill on the conversion.
The mechanics matter. Roth conversions are reported on Form 8606 and added to your AGI for the year. You'll owe federal tax (and state tax in most states) on the converted amount when you file. Conservative strategy: pay the tax from outside funds (taxable brokerage or savings) rather than withholding from the conversion itself, so 100% of the conversion ends up in the Roth. Withholding from the conversion reduces the amount that ends up growing tax-free and creates a small inefficiency. The conversion has no income limit — high earners blocked from direct Roth IRA contributions can still convert any amount.
How to start: pull a draft tax return for the current year in October or November. Compare your projected taxable income to the top of each bracket. The 'room' in the 22% or 24% bracket is your maximum conversion amount for the year. Run a conversion of that amount and recompute the tax owed. Set aside cash from outside the IRA to pay the tax bill. Repeat every year through age 72. Run the math against IRMAA tiers and NIIT thresholds. This is one of the few tax moves where the optimal answer is highly personal — and the difference between 'no conversions ever' and 'maxed-out conversions during the window' often exceeds $150,000 of lifetime federal tax savings.
Use the RMD Forecaster on this site to model your specific situation. Input your current Traditional IRA balance, your other income, and a conversion ladder amount. The tool projects year-by-year through age 95 under both scenarios — no conversion vs your ladder — and tells you the lifetime federal tax delta. For most retirees aged 60-72 with $500K+ in Traditional IRAs, the answer is unambiguous: you should be converting. The only question is how much.