Roth Conversion Window Calculator
The years between retirement and your first RMD are often the lowest-tax window of your life. This calculator finds how much you can convert each year — filling your current bracket — without triggering Medicare IRMAA surcharges or jumping into a higher bracket.
How the calculator works
During the pre-RMD window — the years after you stop working but before required minimum distributions begin — your income often drops to its lowest point since early adulthood. That creates headroom inside the 12% and 22% tax brackets that you can fill with Roth conversions.
The calculator finds your bracket headroom: the amount of traditional IRA you can convert each year before the last dollar of conversion moves into a higher bracket. It also checks whether your conversion would breach the first IRMAA Medicare surcharge tier, which for 2026 starts at $109,000 MAGI (single) or $218,000 MAGI (married filing jointly).1
2026 federal income tax brackets
Bracket thresholds are for taxable income (after the standard deduction). Your standard deduction reduces taxable income before the brackets apply: $32,200 for married filing jointly, $16,100 for single filers.2
| Rate | Taxable income — MFJ | Taxable income — Single |
|---|---|---|
| 10% | up to $24,800 | up to $12,400 |
| 12% | $24,801–$100,800 | $12,401–$50,400 |
| 22% | $100,801–$211,400 | $50,401–$105,700 |
| 24% | $211,401–$399,900 | $105,701–$197,300 |
Source: IRS Rev. Proc. 2025-32 (2026 inflation adjustments).2
IRMAA: the hidden cost of over-converting
IRMAA is Medicare's income surcharge. For 2026, crossing the Tier 1 threshold by even $1 adds $81.20/month per person to your Part B premium — an extra $974/year each, $1,948/year for a couple. The surcharge applies to your entire premium, not just the income over the line.
Roth conversions count as ordinary income and raise your MAGI. Crucially, IRMAA is based on your income from two years prior — your 2026 conversions affect your 2028 Medicare premiums. The calculator flags whether your target conversion would cross the first IRMAA tier and shows you the IRMAA-safe maximum.
RMD age: when the window closes
Under SECURE 2.0, RMD age depends on your birth year:3
- Born 1951–1959: RMDs begin at age 73
- Born 1960 or later: RMDs begin at age 75
The window is the years from now until your RMD start year. The calculator counts those years and multiplies your annual conversion by the window length to show total conversion potential — assuming a flat income profile for simplicity (growth in your traditional IRA over the window would allow larger conversions over time as the balance grows).
When to fill the 12% vs. 22% bracket
The right bracket target depends on your view of future marginal rates on the IRA money if you don't convert it:
- Fill the 12% bracket when you expect future RMDs plus SS income to land in the 12–22% range. Converting today at 12% instead of withdrawing at 22% later creates a permanent tax saving.
- Fill the 22% bracket when your projected RMD (based on current balance) would push you into the 24–32% range. Paying 22% today is better than 28–32% in your 70s after SS + RMDs stack up.
- Stay IRMAA-safe if you're within a few years of Medicare enrollment and your conversion would breach a surcharge tier — the $974/year cost per person can offset the bracket savings, especially on smaller conversions.
The fastest way to estimate your future RMD bracket: take your projected traditional IRA balance at age 73 or 75, divide by the Uniform Lifetime Table divisor for that age (26.5 at 73, 24.6 at 75), and add your projected SS income. That's a rough estimate of your taxable income in your first RMD year, before any Roth conversions. Our RMD Planning Guide walks through this with worked examples and the full ULT table.
Model your specific Roth conversion strategy
The calculator shows bracket headroom. A retirement income specialist goes further: year-by-year conversion amounts optimized against your projected SS income, pension, RMD schedule, spending, and tax situation — to find the exact amount that minimizes lifetime taxes across your entire retirement.
Related guides and tools
- Roth Conversion Window Guide — the pre-RMD bracket arbitrage strategy with worked married-couple example
- RMD Planning Guide — SECURE 2.0 ages, ULT divisor table, the SS income cascade, and 5 strategies to reduce RMDs
- Medicare IRMAA Planning Guide — complete 2026 tier table, IRMAA avoidance strategies, and the SSA-44 appeal process
- Tax-Efficient Withdrawal Order — which accounts to draw from first and why the conventional order costs most retirees thousands
- Retirement Income Sustainability Calculator — will your savings last? 40-year projection across three return scenarios
- Safe Withdrawal Rate Guide — the 4% rule, Guyton-Klinger guardrails, and how spending flexibility changes everything
- Centers for Medicare & Medicaid Services. "2026 Medicare Parts A & B Premiums and Deductibles." CMS Fact Sheet, November 2025. 2026 IRMAA thresholds and Part B premium tiers. cms.gov. Confirmed: Tier 1 starts at $109,000 (single) / $218,000 (MFJ).
- IRS Rev. Proc. 2025-32. "2026 Inflation Adjustments." Standard deduction: $32,200 MFJ / $16,100 single. Tax bracket thresholds: 12% bracket top $100,800 MFJ / $50,400 single; 22% bracket top $211,400 MFJ / $105,700 single. IRS Rev. Proc. 2025-32 (PDF).
- SECURE 2.0 Act of 2022, §107. RMD age raised to 73 for taxpayers born 1951–1959; raised to 75 for taxpayers born 1960 or later. Effective for distributions in 2023 and later tax years. IRS RMD overview.
- IRS Publication 590-B (2025). "Distributions from Individual Retirement Arrangements." Uniform Lifetime Table for calculating RMDs, including divisor 26.5 at age 73 and 24.6 at age 75. IRS Pub. 590-B. Also: Kitces, M. "Understanding the Uniform Lifetime Table for RMD Calculations." Kitces.com.
Calculator uses 2026 federal tax brackets and IRMAA thresholds from IRS Rev. Proc. 2025-32 and CMS. Assumes standard deduction only; does not model itemized deductions, additional senior deductions, AMT, state income tax, or the SS provisional income formula. Social Security provisional income can effectively raise marginal rates — if you're receiving SS, consult an advisor for precise conversion sizing. Values verified April 2026. Not tax or investment advice.