Roth Conversion Tax Impact Calculator
Model the tax impact of converting traditional IRA or 401K funds to a Roth IRA. See the break-even point and long-term tax savings.
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Advanced Conversion Tax Analysis 2026 BRACKETS
⌄Personalized conversion tax calculation appears after you Calculate
Bracket-Fill Optimization — Convert Exactly To The Top Of Your Target Bracket
The optimal conversion amount fills your current bracket exactly — no more, no less. Crossing into the next bracket pays a higher rate; staying short of the bracket top leaves "space" unused. The math below shows the exact conversion ceiling for each scenario.
| Bracket top | $103,350 |
| Other income | $65,000 |
| Available bracket space | $38,350 |
| Federal tax on conversion | $8,437 |
| Effective rate on conversion | 22.0% |
2026 Federal Bracket Tops (MFJ)
| Bracket | Top of Bracket (MFJ) | Top of Bracket (Single) | Conversion Strategy |
|---|---|---|---|
| 10% | $23,850 | $11,925 | Fill if available — almost free conversion |
| 12% | $96,950 | $48,475 | Optimal target for most retirees |
| 22% | $206,700 | $103,350 | Common ceiling; watch IRMAA at $218K MFJ |
| 24% | $394,600 | $197,300 | Acceptable if comparing to 32%+ RMDs |
| 32% | $501,050 | $250,525 | Generally don't convert at this rate |
| 35% | $751,600 | $626,350 | Almost never optimal |
| 37% | — | — | Never convert at top bracket |
2026 brackets per IRS Notice 2025-67. The "fill the bracket" strategy is universally recommended in tax-planning literature (Kitces, Pfau, Vanguard). Standard deduction ($31,500 MFJ / $15,750 single in 2026) is automatic — taxable income is what matters here, not gross income.
State Tax on Conversion — Up to 13.3% Extra You Probably Forgot
A Roth conversion is treated as ordinary income for federal tax — but most states tax it identically at your state marginal rate. States with no income tax have a huge advantage for conversion timing: a $200K conversion in California costs an extra $24K-$26K in state tax that's $0 in Florida or Texas.
| State Group | Conversion Tax Rate | $100K Conversion State Cost | Strategy |
|---|---|---|---|
| 9 no-income-tax states (TX, FL, WA, NV, SD, WY, AK, TN, NH) | 0% | $0 | Convert freely; pure federal-only tax |
| Low-tax states (PA, IL, MI, IN — flat 3-5%) | 3-5% | $3,000-$5,000 | Convert at favorable federal brackets |
| High-tax states (NY, NJ, MA, OR — 6-9.85%) | 6-9.85% | $6,000-$9,850 | Time conversion before any state move |
| California (top tier) | 13.3% + 1% MHST | $13,300+ ($1,000 extra above $1M) | Strongly consider deferring until residency change |
Establishing residency for tax purposes
- Domicile change requires proving intent to establish a new permanent home, not just visiting. CA in particular aggressively challenges residency departures.
- 183-day rule applies in many states — physical presence matters. Track days carefully.
- Other indicia: driver's license, voter registration, bank accounts, doctor of record, vehicle registration, real estate, club memberships.
- Don't trigger residency in two states. Some states (CA) consider you a partial-year resident for any period of physical presence.
- Source-state taxation: Conversion of an IRA originally funded with CA-source income may still be subject to CA tax even after move (rarely enforced for IRA-only situations, but possible).
CA conversion taxation for non-residents per CA FTB domicile rules. The "source-state taxation" issue is more relevant for pension and stock-comp than IRAs. For most retirees, simply establishing legitimate domicile in the new state before converting is sufficient.
The IRMAA 2-Year Lookback — Conversion Now Hits Medicare Premiums Later
Your 2026 Medicare premiums are based on your 2024 MAGI. Your 2028 Medicare premiums are based on your 2026 MAGI. A Roth conversion done in 2026 affects your Medicare bill in 2028 — surprising many retirees who don't realize the connection. The cliff structure makes this especially painful: $1 over a threshold triggers the FULL surcharge for that tier.
| Conversion Year | Determines IRMAA For | Practical Implication |
|---|---|---|
| Age 63 (2026) | Age 65 IRMAA (2028) | First year you're on Medicare — first IRMAA hit |
| Age 64 (2027) | Age 66 IRMAA (2029) | Still feels lookback effect for 2 years |
| Pre-age-63 (62 or earlier) | No IRMAA impact | Lookback ends before Medicare starts — convert freely |
| Age 70+ (2033) | Age 72 IRMAA (2035) | Continuing IRMAA exposure unless income drops |
2026 IRMAA cliff costs (couple, both Medicare)
| 2026 IRMAA Tier | Single MAGI | MFJ MAGI | Annual Cost ($1 over threshold) |
|---|---|---|---|
| Tier 0 → Tier 1 | $109K cliff | $218K cliff | +$2,297 (couple) |
| Tier 1 → Tier 2 | $137K cliff | $274K cliff | +$3,475 additional |
| Tier 2 → Tier 3 | $170K cliff | $340K cliff | +$3,455 additional |
| Tier 3 → Tier 4 | $205K cliff | $410K cliff | +$3,455 additional |
| Tier 4 → Tier 5 | $500K cliff | $750K cliff | +$1,234 additional (smaller jump) |
2026 IRMAA brackets per CMS / Kiplinger. Each spouse on Medicare pays the surcharge individually (couple costs reflect both spouses). For single filers, divide the couple costs by 2. Use Form SSA-44 only for legitimate "life-changing events" (retirement, divorce, etc.) — Roth conversions don't qualify.
NIIT & AMT — Two Hidden Surcharges Most People Miss
A conversion isn't directly subject to 3.8% Net Investment Income Tax (NIIT) — conversion income is ordinary, not investment income. BUT, the conversion raises your MAGI, which can push your OTHER investment income (dividends, capital gains, rental) into NIIT territory. The thresholds — set in 1986 and never inflation-adjusted — are now hit by many middle-income retirees.
| Tax/Surcharge | Threshold (Single) | Threshold (MFJ) | Rate | Applies To |
|---|---|---|---|---|
| NIIT (Net Investment Income Tax) | $200,000 | $250,000 | 3.8% | Investment income (NOT conversion itself) |
| Additional Medicare Tax | $200,000 | $250,000 | 0.9% | Wages above threshold (rare for retirees) |
| AMT (Alternative Min Tax) | $612,000 exemption start | $1,224,000 | 26-28% | Rarely triggers post-OBBBA |
The NIIT thresholds NEVER adjust for inflation
NIIT was enacted in 2010 (effective 2013) at $200K/$250K thresholds. Unlike income tax brackets, these are statutory and have never been inflation-adjusted. In 2013 dollars, these were "high earner" thresholds. In 2026, $250K MFJ is firmly upper-middle-class. By 2030, the same thresholds will hit even more retirees — making NIIT awareness increasingly important for conversion planning.
AMT after OBBBA — mostly defanged
The Alternative Minimum Tax was a major issue under pre-2018 rules but was largely neutralized by TCJA's higher exemptions and phase-outs. OBBBA (2025) made these exemptions permanent, so AMT now affects very few taxpayers (<0.1%, vs. 3-5% before 2018). For most conversion planners, AMT can be ignored — verify with a tax pro if you have unusual deductions or large state-tax bills.
NIIT per IRC §1411. AMT 2026 exemptions per IRS Notice 2025-67 (kept at $87,200 single / $135,200 MFJ before phase-outs, with phase-outs extended permanently under OBBBA). Source on hidden tax interactions: Michael Kitces tax-planning library.
Social Security Taxability — The Trap That Catches Older Converters
If you're already receiving Social Security, a Roth conversion adds to your "provisional income" — potentially making more of your SS benefits taxable. The thresholds were set in 1983 and 1993 and have NEVER been adjusted, so they're now extremely low. Many retirees inadvertently double-tax themselves: paying conversion tax AND making SS benefits taxable.
| Filing Status | Provisional Income Threshold | SS Benefit Taxable |
|---|---|---|
| Single — under $25,000 | $25,000 | 0% |
| Single — $25,000 to $34,000 | $25K-$34K | Up to 50% of benefits taxable |
| Single — over $34,000 | $34,000+ | Up to 85% of benefits taxable |
| MFJ — under $32,000 | $32,000 | 0% |
| MFJ — $32,000 to $44,000 | $32K-$44K | Up to 50% taxable |
| MFJ — over $44,000 | $44,000+ | Up to 85% taxable |
The "tax torpedo" — why this hits hard
When a conversion bumps a portion of SS benefits from 50% taxable to 85% taxable, your effective marginal tax rate on the conversion can be much higher than your nominal bracket. Example: MFJ couple in 22% bracket converts $20K. The conversion adds $20K to AGI, plus pulls another $7K of SS benefits into 85% taxability. Effective marginal rate: 22% × ($20K + $7K) / $20K = ~30% effective, not 22% nominal. This phenomenon is called the "Social Security tax torpedo."
Strategy: convert BEFORE claiming SS
- Convert in the gap years (60-70 if you delay SS to 70). No SS = no SS taxability complications.
- Delay SS to 70 to maximize benefits AND extend the conversion-friendly window.
- If already on SS: the conversion still often makes sense, just compute the all-in effective rate carefully — including the SS torpedo effect.
- Consider a one-year "torpedo year": some advisors recommend taking the SS taxability hit in one large conversion year, then keeping income low afterward to push SS back to 50% taxable in subsequent years.
SS taxability thresholds per IRC §86 (set in 1983 with 50% threshold; 85% added in 1993). Both have never been inflation-adjusted — Congress would need to act to change them. The tax torpedo phenomenon is documented extensively in academic literature; see Kitces.com and Bogleheads wiki on SS taxation.
Continue your conversion decision
Things to Know
Essential concepts for understanding your results
Tax CalculationHow much tax will you owe on a Roth conversion?
The converted amount is added to your ordinary income for the year. Converting $40,000 while earning $60,000: total taxable income = $100,000. After standard deduction ($15,000 single): $85,000 taxable, placing you in the 22% bracket. Tax on the conversion: approximately $6,800-8,800 depending on how much falls in the 12% vs 22% bracket. Always pay tax from non-IRA funds — using IRA money to pay reduces the conversion amount and may trigger a 10% penalty if under 59½.
Bracket FillingWhat is the bracket-filling strategy?
Convert just enough to fill your current tax bracket without pushing into the next one. If single with $45,000 taxable income (12% bracket ends at $47,150): convert only $2,150 at 12%. Or fill the 22% bracket up to $100,525: convert $55,525 at a blended rate. The optimal conversion amount fills the bracket where conversion tax is lower than your expected future RMD tax rate. A financial advisor or tax software can model exact amounts.
Multi-Year PlanningShould you spread conversions over multiple years?
Almost always yes. A $400,000 conversion in one year would push deep into the 32-37% bracket. Spreading it as $50,000-80,000/year over 5-8 years keeps most conversions in the 22-24% bracket — saving $20,000-60,000 in taxes compared to a single large conversion or waiting for forced RMDs. The ideal conversion window: retirement to age 73, when income is lowest. Each year is an opportunity to fill low brackets with converted dollars.
State Tax ImpactHow do state taxes affect the conversion decision?
Conversions are taxed by your state of residence at the time of conversion. If you plan to relocate to a no-income-tax state (FL, TX, NV, TN, WY, SD, WA, AK, NH), consider waiting to convert until after the move — saving 4-13% in state taxes. A $50,000 conversion in California (9.3% rate at that income) costs $4,650 in state tax. The same conversion in Texas: $0. For large balances, this state arbitrage is worth $10,000-50,000 in lifetime tax savings.
How Roth Conversion Taxes Are Calculated
When you convert Traditional IRA or 401(k) funds to a Roth IRA, the converted amount is added to your taxable income for that year. You pay ordinary income tax on every dollar converted — no special rate, no capital gains treatment. A $50,000 conversion for someone already earning $80,000 adds to their taxable income, potentially pushing the top portion into the 24% bracket.
The tax calculation: Start with your regular taxable income (wages, business income, etc. minus deductions). Add the conversion amount. Apply the progressive tax brackets to the total. The incremental tax from the conversion is the cost of converting. On $80,000 taxable income (22% bracket) with a $40,000 conversion: the first $23,350 of the conversion fills the 22% bracket ($5,137 tax), the remaining $16,650 enters the 24% bracket ($3,996 tax). Total conversion tax: $9,133 — an effective rate of 22.8% on the $40,000.
Critical rule: Pay the tax from a separate account (checking, taxable brokerage) — NOT from the converted amount. If you convert $50,000 and withhold $11,000 for taxes, only $39,000 reaches your Roth. The $11,000 withheld is treated as a distribution — subject to 10% early withdrawal penalty if you are under 59½. Always pay conversion taxes externally to maximize the Roth balance and avoid penalties.
The Bracket-Filling Strategy: Optimal Conversion Amount
The most tax-efficient approach: convert exactly enough to fill your current bracket without spilling into the next one. This maximizes dollars converted at the lowest available rate.
2026 example — Married couple, early retirement: Combined income from part-time work: $30,000. Standard deduction: $32,200. Taxable income before conversion: $0 (income below standard deduction). They can convert $23,850 at 10% ($2,385 tax) + $73,100 at 12% ($8,772 tax) = $96,950 total converted at an effective rate of only 11.5%. That is $96,950 moved from a tax-deferred account (future 22-24% tax) to tax-free Roth at an 11.5% rate — saving $10,000-$12,000 in future taxes on that batch alone.
Repeat this each year during the conversion window (early retirement before Social Security and RMDs begin). Over 5-7 years of bracket-filling conversions: $500,000-$700,000 moved to Roth at 10-12% rates, avoiding 22-32% rates on future RMDs. The cumulative tax savings: $50,000-$100,000+.
Hidden Tax Impacts of Roth Conversions
The federal income tax on the conversion is the obvious cost. But several secondary effects can significantly increase the true cost if not anticipated:
Medicare IRMAA surcharges: Conversion income increases your Modified AGI. If it exceeds $206,000 (married) in 2026, you face Income-Related Monthly Adjustment Amounts — higher Medicare Part B and Part D premiums for 2 years (IRMAA uses 2-year-lookback). The surcharge can add $70-$400+/month per person. Large conversions near the IRMAA threshold need careful sizing.
Social Security taxation: Conversion income counts toward the "combined income" formula that determines how much of your Social Security is taxable. A conversion that pushes combined income above $32,000 (single) or $44,000 (married) can trigger 85% of SS benefits becoming taxable — the so-called "tax torpedo."
ACA premium subsidy loss: For early retirees on ACA marketplace insurance, conversion income increases MAGI, which can reduce or eliminate premium tax credits. A $40,000 conversion could cost $4,000-$8,000 in lost ACA subsidies — sometimes exceeding the income tax on the conversion itself. Model the ACA impact before converting.
State taxes: Most states tax Roth conversions as ordinary income. If you plan to retire in a no-tax state, consider waiting to convert until after the move — saving 5-13% in state taxes on the entire conversion. For a $500,000 total conversion plan, the state tax savings from relocating first could be $25,000-$65,000.
Roth Conversion Tax Planning by Life Stage
Working years (high income): Generally not the time for large conversions — your income already fills the higher brackets. Small conversions to Roth 401(k) may make sense if you expect to be in the same or higher bracket in retirement. Backdoor Roth IRA contributions ($7,000/year) are always appropriate regardless of income.
Gap years (between careers, sabbatical): Temporarily low income creates a conversion window. If taxable income drops to $20,000 for a year, you can convert $28,000-$77,000 at the 10-12% rate before returning to your normal bracket. One gap year of strategic conversion can save $5,000-$15,000 in lifetime taxes.
Early retirement to 72 (the golden window): The most valuable conversion period. Income is low (no salary), Social Security has not started, and RMDs have not begun. 5-10 years of systematic bracket-filling conversions can eliminate the majority of your Traditional IRA before RMDs force withdrawals at potentially higher rates.
After RMDs begin (73+): Conversions are still possible but less efficient — RMD income fills the lower brackets first, so conversions stack on top at higher rates. The window narrows but does not close entirely. Small annual conversions may still make sense if your RMDs do not fill your bracket completely.
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