The Roth Conversion Window: Why the Years Before Social Security and RMDs Are the Most Valuable Tax Planning Years of Retirement
By Novak Financial Partners · Updated May 2026
Key takeaways
- The Roth conversion window is the gap years between retirement (typically age 60 to 65) and the start of Required Minimum Distributions (age 73 or 75). For most retirees this is 5 to 12 years of unusually low taxable income.
- A couple retiring at 63 with $2 million in a traditional IRA can convert roughly $1.29 million over 10 years and save over $160,000 in lifetime taxes, per a 2026 analysis from 24/7 Wall St.
- Convert before claiming Social Security. Once benefits start, the provisional income calculation can make up to 85 percent of your benefits taxable, multiplying the effective marginal rate on a conversion to as high as 49.95 percent
- Roth conversions permanently shrink future RMDs, which keeps you out of higher brackets later and reduces the tax on whatever Social Security benefit you do receive
- The four costs that limit how aggressive you can be: IRMAA Medicare surcharges, the 3.8 percent Net Investment Income Tax, Social Security taxation, and state income tax. Most conversion mistakes happen at the IRMAA brackets
Most retirees stop earning sometime between 60 and 65. Social Security may not start for another five to ten years, depending on when they claim. Required Minimum Distributions do not begin until age 73 or 75. In the years between, taxable income drops to a level it will not see again. The IRS is offering a discount, and most retirees do not realize it is on the table.
This is the Roth conversion window. For most retirees, it is the single most valuable tax planning opportunity of their entire lives. The window does not come with a deadline or a notification. Nothing forces anyone to act on it. The retirees who use it correctly can save tens or hundreds of thousands of dollars in lifetime taxes. The ones who let it pass quietly often do not realize what they missed until RMDs hit and the bill arrives.
This article covers what the conversion window actually is, the math on how much you can convert and at what rate, the four costs that limit how aggressive you should be, and why claiming Social Security closes the window faster than most retirees expect.
What the Roth conversion window actually is
A Roth conversion moves money from a traditional IRA or 401(k) into a Roth IRA. The converted amount is taxed as ordinary income in the year you convert. Once in the Roth, the money grows tax-free, and qualified withdrawals are tax-free in retirement. No Required Minimum Distributions ever apply to the original owner.
The conversion window is the period when doing this trade looks unusually attractive. Three things converge:
Earned income has stopped. You retired. The W-2 wages that put you in a 24, 32, or 35 percent federal bracket are gone.
Social Security has not started yet. If you are delaying benefits to 70 (which most high earners should consider), your taxable income from Social Security is zero.
RMDs have not begun. For anyone born in 1960 or later, RMDs do not start until age 75. For 1951 to 1959, age 73. The IRS is not forcing you to pull taxable income from your IRA yet.
In a typical year during the window, a retired couple might have $30,000 to $80,000 of taxable income from dividends, interest, capital gains, and any planned IRA withdrawals. That puts them in the 12 or 22 percent federal bracket. Compare that to the 24 to 35 percent bracket they were probably in during their working years, or the 24 to 32 percent bracket they will be back in once Social Security and RMDs stack on top of each other.
The gap is the opportunity. Every dollar you convert during the window pays tax at a rate you may never see again. That dollar then grows tax-free forever and never appears on a future tax return.
A worked example: $2 million IRA, retiring at 63
Consider a couple retiring at 63 with $2 million in a traditional IRA. They plan to delay Social Security until 70. Under SECURE 2.0, their RMDs do not begin until age 75. That gives them a 12-year conversion window.
Without any conversions, the $2 million grows at a hypothetical 6 percent. By age 75, it is worth over $4 million. At that point, RMDs start at roughly 4 percent of the balance, climbing each year, generating $160,000 or more in annual taxable income. Stacked on top of Social Security and any pension income, this can push the couple into the 24 or 32 percent federal bracket and trigger significant Medicare surcharges (IRMAA) and Social Security taxation.
Now consider the same couple doing systematic conversions. By converting up to the top of the 22 percent federal bracket each year (roughly $129,000 of conversion income for a married couple in 2026, while staying below the $212,000 IRMAA threshold), they can move approximately $1.29 million over 10 years from traditional to Roth.
Per a 2026 analysis from 24/7 Wall St., this strategy can save over $160,000 in lifetime taxes compared to letting the IRA grow untouched and facing the $160,000+ annual RMD at 75. The savings come from three places: paying tax at 22 percent today instead of 24 to 32 percent later, shrinking the future RMDs that drive Social Security taxation, and locking in the lower bracket before the One Big Beautiful Bill Act senior deductions phase out after 2028.
Hypothetical illustration. Actual conversion benefits depend on individual circumstances including bracket structure, IRMAA thresholds, state taxation, and investment returns. Consult a qualified tax professional before implementing.
Why claiming Social Security closes the window faster than people expect
A typical retiree assumes the conversion window runs from retirement to RMD age. Social Security claiming is treated as a separate decision. This is the most expensive misconception we see.
When Social Security benefits start, they are added to a calculation called provisional income (also called combined income). Provisional income equals your adjusted gross income, plus tax-exempt interest, plus half of your Social Security benefit. Based on the result, up to 85 percent of your Social Security benefit becomes taxable.
Here is why this matters for conversions: a Roth conversion adds taxable income, which increases provisional income, which can push more of your Social Security benefit into the 85 percent taxable tier. You end up paying tax on the conversion AND triggering additional tax on benefits that would otherwise have been partially or fully untaxed.
The effective marginal rate on the conversion can climb to 1.85 times the headline rate. At the 22 percent federal bracket, the effective rate can run 40.7 percent. At the 32 percent bracket, the effective rate can hit 59.2 percent. At the top of the brackets, the math is even worse. National Tax Tools cites an effective marginal rate ceiling of 49.95 percent for typical retirees (37 percent ordinary rate times 1.85 multiplier) when stacking conversions on top of Social Security income.
The bottom line
Convert BEFORE claiming Social Security. Once benefits start, the tax torpedo cuts the math on conversions by roughly half.
The strategic move for many retirees is to delay Social Security to 70 (which itself increases the future benefit by 8 percent per year), and use those gap years to do the bulk of lifetime conversions.
The four costs that limit how aggressive you should be
The conversion window is generous, but it is not unlimited. Four costs determine how much you can comfortably convert in any given year.
1. IRMAA Medicare surcharges. Crossing an IRMAA threshold by even one dollar bumps your Medicare Part B and Part D premiums two years later. The 2026 thresholds start at $106,000 single and $212,000 married. The next bracket up adds roughly $850 per year per person in premium surcharges. A $5,000 over-conversion that crosses a threshold can cost more in IRMAA than it saves in tax. This is the most common mistake we see.
2. The 3.8 percent Net Investment Income Tax. NIIT kicks in at $200,000 single and $250,000 married filing jointly. It does not apply to the conversion itself (which is ordinary income), but it does apply to any investment income above the threshold. A conversion that pushes your AGI above the threshold can trigger NIIT on dividends, capital gains, and interest that would otherwise have been below the line.
3. Social Security taxation. Covered above. The provisional income calculation makes up to 85 percent of benefits taxable once income crosses certain thresholds, multiplying the effective marginal rate on conversions for anyone already receiving benefits.
4. State income tax. Most states tax Roth conversions as ordinary income at full state rates. California and New York add 9.3 to 13.3 percent on top of the federal cost. If you plan to retire in a no-income-tax state (Texas, Florida, Tennessee), waiting until after the move to convert can save the state portion entirely. If you plan to stay in a high-tax state, converting before retirement may sometimes make more sense, because state tax in retirement may be lower depending on your pension treatment and other state-specific rules.
Bracket-fill strategy: how much to convert each year
The cleanest approach to conversions during the window is called bracket-fill. The idea is simple: convert exactly enough each year to reach the top of your current marginal tax bracket without spilling into the next one.
For a married couple in 2026:
| Bracket | Top of bracket (taxable income, MFJ) | Stay below for IRMAA |
|---|---|---|
| 12% | $96,950 | $212,000 |
| 22% | $206,700 | $212,000 |
| 24% | $394,600 | $266,000 |
| 32% | $501,050 | $334,000 |
| 35% | $751,600 | $400,000 |
For most retirees in the gap years, the 22 or 24 percent bracket is the right target. Filling the 22 percent bracket while staying below the $212,000 IRMAA threshold often leaves $80,000 to $130,000 of conversion room per year, depending on other income.
The strategy works best as a multi-year plan. A single $500,000 conversion in one year would push almost any retiree into the 35 percent bracket and trigger maximum IRMAA. The same $500,000 spread across 5 years at $100,000 per year stays in the 22 to 24 percent bracket and may avoid IRMAA entirely. Same total converted, dramatically different tax bill.
Common mistakes we see
Waiting until RMDs start. Every year that passes without conversions is bracket space permanently lost. Once RMDs begin, they push the retiree into a higher bracket, and the conversion window effectively closes.
Converting too aggressively in a single year. A $300,000 single-year conversion that crosses two IRMAA brackets and pushes the retiree into the 32 percent bracket often saves less in long-term tax than the IRMAA, NIIT, and bracket cost it triggers. Spread it across multiple years.
Ignoring the IRMAA two-year lookback. Your 2026 income determines your 2028 Medicare premium. If you convert aggressively in 2026 and start Medicare in 2028, you pay surcharges on a conversion you did two years earlier. Plan around this.
Paying the conversion tax from the IRA. This shrinks the Roth balance and triggers a 10 percent penalty if under age 59 and a half. The conversion math only works cleanly when the tax is paid from outside funds.
Converting after claiming Social Security. The tax torpedo. The effective marginal rate on conversions roughly doubles once benefits start. Most retirees should convert before claiming, even if it means delaying benefits.
Treating the window as optional. The window closes whether you use it or not. Every unused year of low-bracket conversion space disappears.
Frequently asked questions
What is the Roth conversion window?
The Roth conversion window is the gap years between retirement and the start of Required Minimum Distributions (age 73 for those born 1951 to 1959, age 75 for those born 1960 and later). For most retirees, this gap is 5 to 12 years. During this window, earned income has stopped, Social Security may not have started yet, and RMDs have not begun, which often puts you in the lowest tax brackets you will see for the rest of your life. This makes it the single most valuable tax planning opportunity in retirement.
When is the best time to do a Roth conversion?
For most retirees, the best time is during the gap years between retirement and Required Minimum Distributions, when taxable income is at its lowest. Wages have stopped, Social Security may be delayed, and RMDs have not yet begun. This creates room to fill lower tax brackets at known rates. Converting before claiming Social Security is especially important because Social Security income triggers the provisional income calculation, which can push the effective marginal rate on conversions as high as 49.95 percent.
How much should I convert to a Roth IRA each year?
The standard approach is bracket-fill: convert enough each year to fill the top of your current tax bracket without spilling into the next one. For a couple retiring at 63 in the 22 percent bracket, that might mean $40,000 to $80,000 of conversions per year. The 24/7 Wall St. analysis cites a couple retiring at 63 with $2 million in a traditional IRA who can convert roughly $1.29 million over 10 years and save over $160,000 in lifetime taxes by staying below the $218,000 MAGI threshold that triggers IRMAA Medicare surcharges. The right number for your situation depends on your bracket, your IRMAA thresholds, and your other income sources.
Should I delay Social Security to do Roth conversions?
Often, yes. Delaying Social Security from full retirement age to 70 widens your Roth conversion window and increases your future benefit by 8 percent per year. Once Social Security starts, the provisional income calculation makes up to 85 percent of your benefits taxable, which multiplies the effective marginal rate on any conversion you do. Converting before claiming benefits keeps the math clean. The trade-off is giving up Social Security income during those years, which means you need other assets to live on while converting. We covered the full delay decision in our companion piece on when to take Social Security.
Will a Roth conversion affect my Medicare premiums?
Yes, two years later. Roth conversion income counts toward your modified adjusted gross income, which determines your IRMAA (Income Related Monthly Adjustment Amount) Medicare premium surcharge. The 2026 IRMAA thresholds start at $106,000 single and $212,000 married filing jointly. Crossing a threshold by even one dollar bumps your Part B and Part D premiums by hundreds per month. The fix is to model your conversions against the IRMAA brackets and stop short of the next threshold. This is one of the most common mistakes we see.
What is the 5-year Roth conversion rule?
Each Roth conversion has its own separate 5-year clock for penalty-free withdrawal of converted principal before age 59 and a half. The clock starts on January 1 of the year you convert, regardless of when in the year the conversion happens. There is also a separate 5-year rule for tax-free withdrawal of earnings on any Roth account, which only matters once. For most retirees over 59 and a half, the 5-year rule is rarely the binding constraint, but it matters if you might need to access converted dollars before age 64 and a half.
Can I undo a Roth conversion if I change my mind?
No. Since the Tax Cuts and Jobs Act of 2018, Roth conversions are irrevocable. You cannot recharacterize (reverse) a conversion the way you could before. This is why getting the math right beforehand matters so much. If markets drop after you convert, you cannot retroactively undo the conversion to lower your tax bill, you can only adjust future years.
Does a Roth conversion count as income for Social Security?
A Roth conversion does not count as earned income, so it does not directly affect your Social Security benefit calculation. The conversion does count as ordinary income for tax purposes, and that income flows into the provisional income calculation that determines what percentage of your Social Security benefit is taxable. This is the tax torpedo: a large conversion in a year when you are also receiving Social Security can push up to 85 percent of your benefits into taxable territory. Converting before claiming Social Security avoids this entirely.
Should I pay the conversion tax from the IRA or from outside funds?
From outside funds, almost always. Paying the tax from the IRA shrinks the amount of money that gets to grow tax-free in the Roth, which is the entire point of the conversion. If you are under 59 and a half, paying the tax from the IRA also triggers a 10 percent early withdrawal penalty on the withheld amount. Having taxable brokerage or cash available to cover the conversion tax is one of the prerequisites for conversions making sense. If you do not have outside funds, the math often gets worse.
When does a Roth conversion not make sense?
A conversion is usually a bad idea if you expect to be in a meaningfully lower tax bracket in retirement than you are today (uncommon for most high earners but possible), if you plan to move from a high-tax state to a no-income-tax state in retirement, if you do not have outside funds to pay the conversion tax, if you need the converted dollars within 5 years (the 5-year clock), or if the conversion would push you across an IRMAA threshold by an amount larger than the long-term tax savings. The conversion math is not universally favorable; it has to be modeled.
Sources
24/7 Wall St., "The Roth Conversion Strategy Affluent Investors Over 60 Are Using to Empty Their 401(k)s" (March 2026). $1.29M conversion and $160K savings figures.
National Tax Tools, "Roth IRA Conversion Tax Strategies 2026 Guide". Provisional income calculation, 49.95 percent effective marginal rate analysis, IRMAA thresholds.
Income Laboratory, "Roth Conversion Strategy 2026: The Advisor's Complete Guide". Bracket-fill methodology and conversion window framing.
Internal Revenue Service, Retirement Plans FAQs Regarding IRAs. Conversion mechanics, irrevocability since 2018, RMD age changes under SECURE 2.0.
Centers for Medicare and Medicaid Services. IRMAA threshold tables for 2026 Medicare Part B and Part D premium calculations.
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See if flat-fee planning is right for youThis article is for educational and informational purposes only and does not constitute personalized investment, tax, legal, or financial planning advice. Tax rates and thresholds are based on current IRS, CMS, and Social Security Administration guidance for 2026 and are subject to change. Hypothetical illustrations including the $1.29M conversion and $160K savings example are based on third-party analysis and assume specific income levels, return assumptions, and tax brackets that will not match every individual situation. Actual outcomes depend on bracket structure, state taxation, IRMAA thresholds, investment returns, and other factors. Consult a qualified financial, tax, or legal professional before implementing any conversion strategy. Roth conversions are irrevocable; the decision cannot be undone. Advisory services are offered through Core Planning LLC, a Registered Investment Advisor. For additional disclosures please visit corepln.com/disclosures.
