Roth Conversion Strategy After Retirement: The BETR Calculation and When It Works

Why Post-Retirement Conversions Are Different From Pre-Retirement Conversions

Pre-retirement conversions happen at the investor's peak earning rate. Post-retirement conversions happen at the lowest. The math, bracket exposure, and planning constraints all change.

The Tradeoff: Paying Tax Now vs. Larger RMDs Later

A Roth conversion is generally taxable in the year it occurs. The balance moves to the Roth side where it generally grows free of further income tax, generally eliminating future RMDs and tax on qualified distributions. The decision generally hinges on comparison: if the retiree's rate today is lower than the rate the same dollars would face later, converting now may be mathematically favorable. Many retirees may underestimate the future rate because RMDs, Social Security, and pension income stack once mandatory distributions begin.

Why the Post-Retirement Window Is Commonly Considered for Conversions

The first two or three years after retirement may often produce a relatively low AGI. Social Security may be deferred to 67 or 70. Pension income may not start until year two. A retiree with a modest pension and no Social Security may sit inside the 12% or 22% bracket. That window generally closes when RMDs begin at 73 or 75 under SECURE 2.0.

The BETR Framework: Vanguard's Break-Even Tax Rate Approach

Vanguard wealth-planning specialists Boris Wong and Joel Dickson developed the break-even tax rate model to give retirees a calculable answer to the conversion-timing question.

What BETR Means and How to Calculate It

BETR is the future marginal rate at which an investor is approximately indifferent between converting now and leaving the balance traditional. If the expected future rate exceeds the BETR, converting today may be more favorable. If it sits below, leaving the balance traditional generally produces the better after-tax outcome. BETR is a simplified framework, and actual outcomes depend on investment performance, tax legislation, and individual circumstances.

Four inputs lower the BETR: paying the conversion tax from capital outside the IRA, basis already inside the IRA from prior after-tax contributions, a longer horizon, and plans for future backdoor Roth contributions. An investor at a 35% current marginal rate who expects to remain at 35% in retirement, paying tax from cash, sees a BETR of roughly 14.1% in Vanguard's illustration (6% return, 20-year horizon). Paying from inside the IRA produces a BETR of ~35%.

BETR Above Your Current Rate: When Converting May Be Favorable

If BETR is 30% and the retiree's current rate is 22%, converting at 22% generally favors the investor, provided the expected future rate sits at or above 30%. Many retirees end up in higher brackets in their late 70s and 80s once RMDs, Social Security, and pension income stack. Filing-status changes after a spouse's death also push the projected rate higher.

BETR Below Your Current Rate: When Waiting May Make More Sense

If BETR is 18% and the current rate is 24%, converting may not favor the investor. A retiree with a small traditional IRA, a long lifespan in a low-bracket state, and no estate-tax exposure may come out ahead leaving the balance traditional. The framework is a decision tool, not a sales argument.

How the NAV Discount May Shift the BETR Calculation

A standard BETR calculation uses the full conversion amount as the taxable base. A discounted conversion of a private real estate interest uses the sponsor-disclosed appraised value reported by the IRA custodian, which sits below the nominal balance under Revenue Ruling 59-60 discounts. The lower taxable base means a lower tax bill at the same marginal rate, functioning as a fourth lever alongside the three Vanguard inputs.

Worked example: a $200,000 conversion at a 24% rate produces ~$48,000 in tax. With a 20% NAV discount, the taxable base drops to $160,000 and the tax bill to ~$38,400. Illustrative savings: $9,600. See the complete guide to discounted Roth conversions for the full mechanics. The same framework applies to anyone expecting a low-income year (parental leave, sabbatical, business startup). BETR is not exclusively a retiree tool.

The IRMAA Problem: How Roth Conversions Interact With Medicare Premiums

Roth conversions raise MAGI in the conversion year, which can push the retiree above an IRMAA threshold and trigger Medicare premium surcharges two years later.

What IRMAA Is and How It Works

IRMAA is a Medicare Part B and Part D premium surcharge for higher-income beneficiaries based on MAGI. The 2026 standard Part B premium is $202.90 per month, with higher-income beneficiaries paying multiples based on tier. Thresholds adjust annually. Verify current figures at Medicare.gov.

Part D carries its own surcharge schedule on the same tiers. A retiree couple on Medicare can see annual cost increases of $2,000 to $11,000 depending on how many tiers a conversion crosses, paid per person.

The Two-Year Lookback Rule and Why It Matters for Conversion Timing

IRMAA is based on MAGI from two years prior. A conversion in 2026 determines 2028 Medicare premiums. Many retirees miss this when modeling conversion costs because the IRMAA increase does not appear on the same year's tax return as the conversion.

Staying Under the IRMAA Threshold vs. Accepting the Surcharge for Long-Term Gain

Staying just under a tier is a legitimate planning goal, but not always worth sacrificing conversion efficiency for. If converting $50,000 above a tier ceiling triggers a Tier 1 surcharge of ~$975/year for two years (single), the two-year cost is ~$1,950. If that conversion saves $8,000 to $12,000 in future RMD tax, the math may favor accepting the surcharge.

How a Discounted Conversion Lowers MAGI and Reduces IRMAA Exposure

A sponsor-disclosed discounted conversion uses a lower custodian-reported value as taxable income, so the MAGI increase is proportionally smaller. A $100,000 nominal conversion at a 25% NAV discount produces a $75,000 MAGI increase, which can be the difference between staying under a tier and crossing it.

Social Security and Provisional Income: The Conversion Tax Trap

Roth conversions do not themselves count as Social Security income, but they increase AGI, which increases provisional income and determines how much of any benefit is taxable.

How Roth Conversions Affect Social Security Taxation

Under IRC Section 86, provisional income equals AGI plus tax-exempt interest plus 50% of Social Security benefits. Above $34,000 (single) or $44,000 (MFJ), up to 85% of benefits become taxable. These thresholds have not been adjusted for inflation since 1984. See IRS Publication 915 for the taxability worksheet.

Coordinating Conversion Timing With the Social Security Claiming Decision

For retirees delaying Social Security to 67 or 70, the years between retirement and claiming are typically the strongest conversion years. Once benefits begin, every additional conversion dollar can pull more of the benefit into taxation, raising the effective marginal rate above the nominal bracket rate.

Worked Case Study: Nancy Converts $350K Into a Ground-Up Multifamily Development LP at a 25% NAV Discount

Consider the following hypothetical for illustrative purposes only. Nancy is 64, single, retired one year ago from a hospital administrator role. She has $350,000 in a traditional IRA, $80,000 in a Roth IRA, and a $28,000 annual pension, with Social Security planned at 67. Her current taxable income sits well inside the 12% bracket, and she has 9 years before her first RMD at 73 under SECURE 2.0.

Her traditional IRA holds a ground-up multifamily development LP interest building a 200-unit Class B apartment community with a 7-year hold horizon. Multifamily development carries higher lack-of-control and lack-of-marketability discounts than stabilized assets because there is no operating income during construction and lease-up and the LP interest is illiquid through stabilization. The sponsor's appraisal firm establishes a 25% NAV discount, within a typical 25 to 40% range for ground-up multifamily development, and reports $262,500 to the custodian on her $350,000 nominal position.

The Baseline: What Happens If Nancy Does Nothing

Compounding at an assumed 6% return, the balance may grow to approximately $590,000 by age 73. Her first RMD would be roughly $22,300. By age 78, the RMD has grown to approximately $41,000 stacked on Social Security and pension. Her MAGI in those years exceeds $100,000, pushing her into the 24% bracket and across the first IRMAA tier. Cumulative federal tax on the RMD stream over a decade may approach $150,000.

The BETR Analysis: Is the Conversion Worth It?

Nancy's current marginal rate is 22% after pension, standard deduction, and a planned $60,000 annual conversion fitting inside the 22% bracket ceiling. Her projected RMD-era rate is 24% to 28%. Because her projected future rate exceeds the BETR, converting at 22% generally favors her. Without a discount, four annual conversions of $60,000 (ages 64-67) produce a taxable basis of $240,000 and approximately $52,800 in federal tax. Remaining traditional balance: roughly $110,000. First RMD at 73: approximately $4,150. See the Roth conversion strategy to avoid RMDs explainer for the full mechanics.

BETR With the NAV Discount: How the Math Changes

Each year's $60,000 nominal conversion would be taxed on a custodian-reported $45,000 basis. Federal tax per year at 22% would be approximately $9,900. Four-year total would be approximately $39,600. Tax savings versus the no-discount path would be approximately $13,200. The same $240,000 of economic value moves to the Roth side, but Nancy would pay tax on $180,000 of basis rather than $240,000.

The IRMAA Constraint: Managing the Conversion to Stay Under the Threshold

Nancy's conversion-year MAGI would be the $45,000 conversion basis plus $28,000 pension, or approximately $73,000. That sits well under the 2026 single-filer IRMAA threshold of $109,000. Without the discount, her MAGI would be $88,000, still under but with less cushion. In this illustration, if the deal exits at year 7 with capital returned plus any potential capital appreciation flowing back to the investor, the proceeds would sit in Nancy's Roth IRA and subsequent qualified distributions would generally be income-tax-free.

Actual tax outcomes depend on individual circumstances. Consult a qualified tax professional before executing any conversion. All investments carry risk, including the loss of principal. Investors should read the risk factors in the private placement memorandum for each offering before investing.

Post-Retirement Conversion Checklist: 7 Questions to Consider Before Converting

Investors may want to work through these seven questions with a CPA and financial advisor.

1. What Is the Investor's Current Effective vs. Marginal Tax Rate?

The conversion is generally taxed at the marginal rate. Investors may want to confirm it after accounting for the projected conversion amount.

2. What Will the Investor's Tax Rate Be at Roth Distribution?

Investors may want to project RMD income, Social Security, pension, and other taxable income in the distribution years. Expected rate and filing-status changes are commonly layered in. See the traditional IRA to Roth conversion explainer.

3. Has IRMAA Exposure on This Conversion Been Calculated?

Conversion-year MAGI may be modeled against IRMAA tier ceilings two years forward. Investors may want to decide whether to stay under the next tier or accept the surcharge for a larger conversion.

4. Has the Social Security Provisional Income Impact Been Modeled?

For investors already collecting, the share of the benefit that becomes taxable when the conversion is added to AGI may be calculated. The effective marginal rate may exceed the nominal bracket rate.

5. What Is the Appraised NAV of the Position Being Converted?

For private real estate interests, investors may want to confirm the sponsor-disclosed custodian value in writing before executing. For publicly traded balances, FMV is generally the closing price on the conversion date.

6. Are Liquid Assets Available to Pay the Tax Bill Outside the IRA?

Paying the conversion tax from capital outside the IRA is generally a consequential input to BETR. Investors may want to confirm outside cash or brokerage assets cover the projected federal and state bill before initiating.

7. What Is the Intended Hold Period, and Does the Deal Exit Timeline Fit the Plan?

The hold period (typically 5, 7, or 10 years) generally sets when capital returns to the Roth side. If the balance is destined for heirs under an inherited IRA Roth conversion under the SECURE Act, the 10-year forced-distribution rule generally applies to non-spouse beneficiaries.

At What Age Does a Roth Conversion Stop Making Sense?

There is no single cutoff age, but the rate-arbitrage math that powers most Roth conversions weakens predictably as an investor moves through five age bands. The framework below uses verified 2026 figures (federal brackets, IRMAA tiers from the CMS 2026 Fact Sheet, the SECURE 2.0 RMD age of 73, and statutory provisional-income thresholds) to map when the strategy generally fits and when it generally does not. Each band closes with a worked example. These are simplified hypotheticals using stated 2026 figures. Actual outcomes depend on individual circumstances; consult a qualified tax advisor.

Age 60-65: The Sweet Spot

This is generally the highest-leverage window. The investor is past 59 1/2 (no early-withdrawal penalty), typically not yet drawing Social Security, not yet on Medicare (so IRMAA is not yet in the cost equation), and frequently sits in a low-income "valley" between when wages stopped and when SS plus RMDs begin. Every conversion dollar at this age may fill a low-rate bracket today and avoid being forced out at a higher rate at 73 or later. Opening the qualified-distribution 5-year clock now also matters, so future earnings come out tax-free.

For illustration purposes, consider a hypothetical investor: age 62, married filing jointly, $80,000 from pension and portfolio dividends. After the 2026 MFJ standard deduction of $32,200, taxable income sits at $47,800, well inside the 12% MFJ bracket (top of 12% MFJ = $100,800). Headroom in the 12% bracket: $53,000. Converting $53,000 at 12% would generate roughly $6,360 in federal tax. If the same $53,000 were instead distributed as an RMD at age 75 inside the 24% bracket (stacked on SS and pension), the tax cost would be roughly $12,720. Rate-arbitrage savings: approximately $6,360 per conversion. Investors who consider offerings that include sponsor-disclosed discounted valuations may potentially affect the effective tax rate on real economic value. This band generally fits.

Age 65-70: Sweet Spot With IRMAA Awareness

The math is still favorable, but Medicare enrollment at 65 introduces IRMAA into the cost equation. Because IRMAA uses a 2-year MAGI lookback (a 2026 conversion shows up on 2028 premiums per SSA Form SSA-44), conversions in this band may need to be sized to land in a specific IRMAA bracket, not just a specific income-tax bracket. The cliff structure (one dollar over a threshold can trigger a full year of higher premiums for both spouses) makes precision more important here than in any other band.

For illustration purposes, consider a hypothetical investor: age 66, MFJ, $120,000 in current SS plus pension plus dividends, 2024 MAGI of $218,000 (right at the first MFJ IRMAA cliff). The next cliff sits at $274,000 MFJ, leaving $56,000 of conversion headroom before crossing into IRMAA bracket 2. Converting $56,000 (blended roughly half at 12%, half at 22%) may produce approximately $11,200 in federal tax. Crossing the cliff would add $1,148.40 per spouse per year ($2,296.80 for the couple) in combined Part B and Part D IRMAA surcharges. Compared to a forced RMD on the same $56,000 at 24% later, savings are roughly $2,200 in income tax plus avoided multi-year IRMAA exposure. This band generally fits with disciplined sizing.

Age 70-73: The Final Window Before RMDs

Last call. The investor is past 65 (so IRMAA is already in the picture) and likely already collecting Social Security. RMDs are about to start at 73 under SECURE 2.0. Every year between now and 73 is one less year to spread conversions before the first-money-out rule applies, meaning the required RMD must come out first and any conversion must layer on top of mandatory RMD income. Many planners aggressively front-load conversions in this window, sometimes accepting a one-bracket-higher rate now to avoid two-bracket-higher rates later.

For illustration purposes, consider a hypothetical investor: age 71, MFJ, $140,000 in current income from SS, pension, and dividends, with a $1.5M traditional IRA balance. Top of the 22% MFJ bracket sits at $211,400, leaving $71,400 of headroom. Converting $71,400 at 22% may generate roughly $15,708 in federal tax. By comparison, waiting until 74 would force a first RMD of approximately $58,500 on the $1.5M balance (at a roughly 3.9% factor), stacked on the existing $140,000 of income, potentially pushing any attempted conversion into the 24% bracket at a tax cost of roughly $17,136. The bigger compounding benefit: moving $71,400 out of traditional now may potentially reduce future RMDs by roughly $2,786 per year. This band generally fits, especially for larger balances.

Age 73-75: First-Money-Out Rule and Diminishing Returns

This is the band where the strategy starts breaking down for most investors. Under IRS Retirement Plan FAQs, once RMDs begin (age 73 for those reaching RMD age between 2023 and 2032), the required distribution must be satisfied before any conversion. Any conversion has to layer on top of RMD income, which may push the household into 24% or 32% brackets and erode the rate-arbitrage premise. The math may still work in two situations: (a) low non-RMD income leaves headroom inside the 22% bracket, or (b) estate planning is the explicit goal because heirs sit in higher brackets and the 10-year inherited-Roth rule changes the calculus.

For illustration purposes, consider a hypothetical investor: age 74, MFJ, $40,000 pension plus $50,000 SS plus $80,000 RMD for $170,000 in ordinary income. Nominal headroom in the 22% bracket exists, but pushing MAGI from roughly $170,000 to $244,000 may cross the $218,000 MFJ IRMAA cliff. Converting only $48,000 to stay below the IRMAA cliff may generate roughly $10,560 in tax at 22%. Rate arbitrage is essentially zero (22% now versus 22% later), so the residual value comes from shrinking the future RMD base, starting the qualified-distribution clock if not yet started, and shifting future asset growth into a tax-free wrapper for heirs. This band generally fits only for estate-planning reasons or unusually low non-RMD income.

Age 75+: When It's Generally Too Late

For most investors the rate-arbitrage math has collapsed by 75. RMDs are large (the Uniform Lifetime Table divisor at 75 is approximately 24.6, at 80 approximately 20.2, meaning a $1M IRA may throw off roughly $40,600 at 75 and $49,500 at 80 before any conversion). Conversions stack on top, frequently pushing income into 24% or 32% brackets. The qualified-distribution 5-year clock, if not previously satisfied, would not pay off on earnings until age 80 or later, an uncertain horizon. The 5 to 7 year horizon typical of private real estate fund interests starts to bump against actuarial life expectancy.

The principal exception is pure estate planning, where heirs are decades from their own RMD age, heirs are in materially higher tax brackets than the retiree, and the retiree has outside liquid capital to pay the conversion tax. For illustration purposes, consider a hypothetical investor: age 76, MFJ, $200,000 in RMD plus SS plus pension income, $1.2M remaining in the traditional IRA, with adult children in the 32% bracket. Converting $50,000 at 24% may generate roughly $12,000 in federal tax. If those dollars instead pass to heirs as a traditional IRA distributed under the 10-year rule at 32%, the family-level tax would be roughly $16,000. Net cross-generational savings: approximately $4,000, plus tax-free growth on the converted balance through to distribution. This band generally does not fit unless wealth transfer to higher-bracket heirs is the explicit goal.

This age framework is the canonical reference used elsewhere in this education library. The discounted Roth conversion pillar, the Roth conversion ladder article, and the when to do a Roth conversion article all reference this section for the age-by-age decision logic. Outcomes vary by individual circumstances. Consult a qualified tax advisor before executing any Roth conversion.

Frequently Asked Questions

Next Steps: Running the BETR Analysis

A post-retirement Roth conversion strategy is generally a sequence of calculations across BETR, IRMAA, and Social Security thresholds. Common action steps include confirming the current marginal rate after the projected conversion, projecting the future RMD-era rate with Social Security and pension stacked, modeling the IRMAA two-year lookback, confirming outside capital for the conversion tax, and reviewing the appraised NAV for any private real estate position. The Roth conversion calculator runs the standard and NAV-discounted tax cost in real time, and the real estate IRA pros and cons overview covers the trade-offs that may help determine whether a private real estate position fits.

Private real estate investments are illiquid securities suitable only for investors with long time horizons. Structural guidance, not tax or investment advice.

Sources

This article references the following IRS publications, Internal Revenue Code sections, and external authorities.

• 26 U.S.C. Section 408A, Roth IRAs (Cornell Law)
• 26 U.S.C. Section 86, Social Security and Tier 1 Railroad Retirement Benefits (Cornell Law)
• 26 U.S.C. Section 401(a)(9), Required Minimum Distribution rules
• IRS Form 8606, Nondeductible IRAs
• IRS Publication 590-A, Contributions to Individual Retirement Arrangements
• IRS Publication 590-B, Distributions from Individual Retirement Arrangements
• IRS Publication 915, Social Security and Equivalent Railroad Retirement Benefits
• Revenue Ruling 59-60, Valuation of Closely Held Stock
• SECURE 2.0 Act of 2022, RMD age changes
• Vanguard BETR methodology, Boris Wong and Joel Dickson, Vanguard
• 2026 Medicare Part B premiums and IRMAA tiers, Centers for Medicare and Medicaid Services