Optimal Roth Conversion Sizing Calculator 2026 β Annual Bracket Fill
Find the optimal annual Roth conversion amount from retirement to age 73. Fill tax brackets each year, avoid IRMAA cliffs, and project Roth balance and lifetime tax savings. 2026 brackets and IRMAA thresholds.
Age 73 per SECURE 2.0 (born 1951β1959), 75 (born 1960+)
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Social Security, pension, dividends, etc.
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Optimal Annual Conversion
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Conversion Window (Years)
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Roth Balance at RMD Age
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Est. Lifetime Tax Savings
Roth Conversion Analysis
Optimal Roth Conversion Strategy
The goal of bracket-fill Roth conversions is to systematically move pre-tax money to Roth accounts during the low-income window between retirement and Required Minimum Distributions, paying lower tax rates now to avoid higher rates later.
Calculation Framework
Conversion Window = RMD Age β Current Age
Bracket Headroom = Bracket Top β (Standard Deduction + Other Income)
Optimal Annual Conversion = min(Bracket Headroom, IRMAA Safe Amount)
Projected Roth at 73 = Annual Conversion Γ FV Annuity Factor(return%, years)
RMD Reduction at 73 = Converted Amounts Γ growth not subject to RMD
Tax Savings = (Future RMD rate β Conversion rate) Γ Total Converted
Bracket Headroom = Bracket Top β (Standard Deduction + Other Income)
Optimal Annual Conversion = min(Bracket Headroom, IRMAA Safe Amount)
Projected Roth at 73 = Annual Conversion Γ FV Annuity Factor(return%, years)
RMD Reduction at 73 = Converted Amounts Γ growth not subject to RMD
Tax Savings = (Future RMD rate β Conversion rate) Γ Total Converted
Example: Age 62, $1.2M pretax, $45K other income, MFJ, fill 22% bracket
Bracket headroom: $206,700 β $30,000 deduction β $45,000 = $131,700/year
IRMAA Tier 1 MFJ: $212,000 β conversion must keep MAGI below $212K
Optimal conversion: $131,700/year Γ 11 years β significant Roth accumulation
Bracket headroom: $206,700 β $30,000 deduction β $45,000 = $131,700/year
IRMAA Tier 1 MFJ: $212,000 β conversion must keep MAGI below $212K
Optimal conversion: $131,700/year Γ 11 years β significant Roth accumulation
Extended
Year-by-Year Conversion Schedule + IRMAA Tier Analysis
Annual conversion amounts, cumulative Roth balance, and IRMAA cliff impact visualization
Year-by-Year Conversion Schedule
| Age | Pre-Tax Balance | Conversion | Tax Paid | Roth Balance (cum.) |
|---|
IRMAA Tier Impact Analysis (2026)
| IRMAA Tier | MAGI (Single) | MAGI (MFJ) | Part B Premium | Annual Surcharge |
|---|
Key insight: Crossing an IRMAA tier can cost $2,000β$8,000/year in extra Medicare premiums. A Roth conversion that pushes you just $1 over a tier triggers the full surcharge for the entire year. Size conversions to stay $5,000β$10,000 below IRMAA thresholds as a safety margin.
Frequently Asked Questions
What is "filling the bracket" with Roth conversions?
Filling the bracket means converting exactly enough traditional IRA/401(k) to Roth to reach the top of your current tax bracket without crossing into the next one. For example, if you are in the 22% bracket with $30,000 of headroom, you convert $30,000 β paying 22% now to avoid the higher future rates you will face on Required Minimum Distributions.
Why is the window between retirement and age 73 so valuable for Roth conversions?
Once you start Required Minimum Distributions at age 73 (SECURE 2.0), you are forced to take taxable withdrawals whether you want to or not. In the years between retirement (when your earned income drops) and age 73, you often have a "window" of artificially low income. Converting in this window lets you pay tax at lower rates than you will face when RMDs force income on you.
How do IRMAA thresholds affect Roth conversion planning?
IRMAA (Income-Related Monthly Adjustment Amount) adds Medicare surcharges when your MAGI exceeds certain thresholds. For 2026: $106,000 single / $212,000 MFJ (Tier 1), $133,000 / $266,000 (Tier 2), etc. Crossing a tier can add $500β$4,000+ per year in Medicare premiums. Roth conversions count toward MAGI for IRMAA, so staying below tier boundaries is critical when sizing annual conversions.
What is the optimal annual conversion amount?
The optimal amount fills the cheapest available bracket without triggering: (1) a higher federal tax bracket, (2) an IRMAA tier jump, (3) taxation of Social Security benefits at a higher rate, or (4) ACA premium credit loss (if applicable). The exact amount depends on your current income, SS benefits, and Medicare enrollment status.
Should I convert if I am in the same tax bracket now and in retirement?
Even at the same rate, Roth conversions can be beneficial if: (1) Your account is large enough that RMDs alone will push you into higher brackets later; (2) You expect tax rates to rise; (3) You have estate planning goals (Roth IRAs pass tax-free to heirs who inherited before SECURE Act); (4) You want to reduce future IRMAA exposure. The best analysis projects your full RMD schedule versus converting now.