Roth Conversion Calculator 2026: Tax, IRMAA and ACA on Every Dollar You Convert
A Roth conversion is taxed now, as ordinary income. What it costs depends on three limits it can cross: the top of your current tax bracket, the first IRMAA threshold (from 63, because of the two-year lookback) and the ACA 400% FPL cliff (before 65, on a marketplace plan). The first calculator below finds the largest conversion under each limit; the second prices a conversion you choose, federal and state, with its IRMAA and ACA effect, using the 2026 brackets and thresholds.
How much tax will I pay on a Roth conversion in 2026?
A conversion is ordinary income for the year you convert: it is taxed at your top federal bracket plus your state’s rate, and while your Social Security is not yet fully taxable, each converted dollar can also make up to 85 cents of benefits taxable. Example: a married couple, 66 and 64, in North Carolina with $40,000 of Social Security and a $30,000 pension who convert $25,000 in 2026 pay $5,081 of federal and $998 of North Carolina tax on it: $6,079, or 24.3% of the amount converted, although they sit in the 10% bracket, because the conversion makes $21,250 more of their Social Security taxable. The next $1,000 they convert costs $262. Only the first $12,729 of a conversion stays in the 10% bracket; $154,000 would bring their 2026 MAGI to the first IRMAA floor (2026 tiers).
| Key number | 2026 |
|---|---|
| Federal tax the conversion adds (Rev. Proc. 2025-32) | $5,081 |
| North Carolina tax it adds (NC rules) | $998 |
| Federal + state tax on the conversion | $6,079 |
| Tax as a share of the $25,000 | 24.3% |
| Social Security the conversion makes taxable (Pub. 915) | $21,250 |
| Tax on the next $1,000 converted | $262 |
| Conversion that stays in the 10% bracket | $12,729 |
| Conversion up to the first IRMAA floor (CMS 2026 tiers) | $154,000 |
| IRMAA MAGI after the $25,000 conversion | $87,350 |
An estimate from QuantCalc’s open tax engine (federal 2.3.2, state 1.14.2) for the 2026 tax year. Not tax advice: your return depends on facts this page does not ask about, so check a move with your tax preparer or custodian before acting. IRMAA: 2026 MAGI sets the 2028 premiums; the 2028 tiers are not published, so the 2026 tiers are shown and indexed tiers will be higher. Whether a conversion is worth its tax depends on the rate you would pay on the same dollars later, which this page does not decide. How the engine computes each line, with its official source: federal, state.
What would a conversion cost you in 2026?
Enter your 2026 and the amount you are thinking of converting. The tax engine prices it: federal and state tax, the Social Security it makes taxable, the 2028 IRMAA tier its MAGI sets and, before 65 on a marketplace plan, the premium tax credit it costs.
Why Roth Conversions Need Optimization
"Convert as much as you can" is dangerously oversimplified. A $5,000 conversion that pushes you $1 over the ACA subsidy cliff can cost $15,000 in lost premium tax credits. A conversion that nudges your MAGI past an IRMAA threshold adds $2,296.80 per year in Medicare surcharges for a couple. The real question is not whether to convert — it is how much to convert each year without triggering penalties that outweigh the benefit.
This calculator models three constraints simultaneously and recommends the smallest — the true safe ceiling for your situation.
The Three Constraints: Tax Bracket, ACA Cliff, IRMAA Threshold
Each constraint operates on your MAGI (ordinary income + conversion amount):
1. Tax Bracket Fill (all ages): Convert enough to fill your current bracket (typically 12% or 22%). Going beyond means paying the next rate on the excess. Rarely the binding constraint for early retirees with modest income.
2. ACA Subsidy Cliff (under 65): ACA premium tax credits vanish entirely when household income exceeds 400% FPL — $62,600 (single) or $84,600 (family of 2) in 2026. This is a cliff, not a slope: one dollar over and you lose the entire subsidy. For ages 55–64, this is often the binding constraint.
3. IRMAA Threshold (ages 63+): IRMAA uses a two-year lookback, so the MAGI you report at 63 sets your Medicare premium at 65 — for most people that is the first premium year a conversion can affect. A conversion at 62 lands on the age-64 premium, which only costs you if you are already enrolled in Medicare that year. The first tier adds $95.70/month per person, Part B plus Part D ($2,296.80/year for a couple, both enrolled). For ages 63–64, both ACA and IRMAA apply simultaneously.
2026 Federal Tax Brackets for Roth Conversions
Roth conversions are taxed as ordinary income stacked on top of your existing income. These are the 2026 federal brackets (post-TCJA reversion did not occur — current rates were extended):
| Rate | Single | MFJ |
|---|---|---|
| 10% | $0 – $12,400 | $0 – $24,800 |
| 12% | $12,400 – $50,400 | $24,800 – $100,800 |
| 22% | $50,400 – $105,700 | $100,800 – $211,400 |
| 24% | $105,700 – $201,775 | $211,400 – $403,550 |
| 32% | $201,775 – $256,225 | $403,550 – $512,450 |
| 35% | $256,225 – $640,600 | $512,450 – $768,700 |
| 37% | Above $640,600 | Above $768,700 |
Standard deduction: $16,100 (single) / $32,200 (MFJ). The 12% bracket is almost always worth filling — paying 12% now to avoid 22%+ later when RMDs stack on Social Security is a strong trade.
The ACA Subsidy Cliff: Why Pre-65 Retirees Must Be Careful
ACA premium tax credits vanish when household income exceeds 400% FPL: $62,600 (single) or $84,600 (family of 2) in 2026. Enhanced subsidies (no cliff) expired end of 2025. Starting in 2026, exceeding the cliff by even $1 means repaying the entire credit — $15,000–$30,000 for a 60-year-old couple. The optimizer caps your conversion to stay safely below.
IRMAA and the Two-Year Lookback Rule
IRMAA surcharges are based on your MAGI from two years prior. A conversion at 63 triggers surcharges at 65. The 2026 thresholds:
| Single MAGI | MFJ MAGI | Monthly Surcharge | Annual / Person |
|---|---|---|---|
| Up to $109,000 | Up to $218,000 | $0 | $0 |
| $109K – $137K | $218K – $274K | +$95.70 | $1,148 |
| $137K – $171K | $274K – $342K | +$240.40 | $2,885 |
| $171K – $205K | $342K – $410K | +$385.00 | $4,620 |
| $205K – $500K | $410K – $750K | +$529.60 | $6,355 |
| Above $500K | Above $750K | +$578.00 | $6,936 |
Surcharges are Part B + Part D combined, per person. For a married couple both on Medicare, crossing the first tier costs $2,296.80/year ($1,148.40 × 2).
The Roth Conversion Sweet Spot: Ages 62–72
The prime Roth conversion window is the decade between early retirement and the start of Required Minimum Distributions. Here is how the constraints shift across these ages:
| Age | Constraints | Typical Binding | Strategy |
|---|---|---|---|
| 55–62 | Bracket + ACA | ACA cliff | Fill bracket up to 400% FPL |
| 63–64 | Bracket + ACA + IRMAA | ACA (usually tighter) | Balance ACA and IRMAA lookback |
| 65–72 | Bracket + IRMAA | IRMAA tier 1 | Fill bracket to IRMAA threshold |
| 73/75+ | Bracket + IRMAA + RMDs | RMDs consume space | Limited conversion room |
RMD start age depends on birth year under SECURE 2.0: 73 for those born 1951–1959, 75 for 1960 and later.
Before 62: widest window, ACA cliff is usually binding. Ages 63–64: both ACA and IRMAA apply. After 65: Medicare replaces ACA, IRMAA becomes binding. At your RMD start age (73 for those born 1951–1959, 75 for 1960 and later): RMDs consume bracket space, leaving little room for voluntary conversions. Every dollar converted in the 12% bracket now avoids 22%+ later when RMDs and Social Security stack together.
Tax Torpedo Interaction
Roth conversions shrink your traditional IRA balance, which means smaller future RMDs, lower provisional income, and less Social Security taxed. The tax torpedo creates effective marginal rates of 22.2%–40.7% when RMDs push provisional income through SS taxation thresholds. Paying 12% now to avoid 22.2%+ in the torpedo zone later is almost always a winning trade.
Use the Tax Torpedo Calculator to model your future torpedo exposure, then use this optimizer to find the conversion amount that eliminates it over time.
Frequently Asked Questions
How much tax will I pay on a Roth conversion?
It is taxed as ordinary income in the year you convert, at your top federal bracket plus your state’s rate, and it can make more of your Social Security taxable. A married couple, 66 and 64, in North Carolina with $40,000 of Social Security and a $30,000 pension pay $5,081 federal and $998 state tax on a $25,000 conversion: $6,079, 24.3% of it. Enter your own year under “What would a conversion cost you in 2026?” for yours.
How much can I convert before the next bracket, IRMAA tier or the ACA cliff?
The calculator above finds the largest conversion that keeps your taxable income inside your current bracket, your MAGI at or below the first IRMAA floor, and (before 65, on a marketplace plan) your income at or below 400% of the poverty line. Those are limits, not a recommendation: whether converting is worth its tax depends on the rate the same dollars would be taxed at later.
How do Roth conversions affect ACA subsidies?
Roth conversions count as ordinary income and increase your Modified Adjusted Gross Income (MAGI). For pre-65 early retirees on ACA marketplace plans, exceeding 400% of the Federal Poverty Level ($62,600 single, $84,600 family of 2 in 2026) means losing all premium tax credits — a cliff that can cost $10,000 to $25,000 in lost subsidies from a single dollar of excess income.
What is the IRMAA two-year lookback and why does it matter?
IRMAA uses your tax return from two years prior to determine your Medicare Part B and Part D surcharges. A large Roth conversion at age 63 will trigger IRMAA surcharges at age 65 when you first enroll in Medicare. The lowest IRMAA surcharge tier adds $95.70 per month per person ($2,296.80/year for a couple), making it critical to plan conversions with the two-year lookback in mind.
Can I still convert after age 65?
Yes. After 65 the ACA cliff no longer applies, but IRMAA does: conversions up to the $109,000 single / $218,000 joint threshold (2026 tiers) add no Medicare surcharge two years later. The room narrows at your Required Minimum Distribution age (73 for those born 1951-1959, 75 for 1960 and later, per SECURE 2.0), when RMDs begin and take up bracket space.
How does conversion room change between 62 and 72?
Before 62: the widest room. Ages 63–64: the IRMAA lookback begins to count. Ages 65–72: IRMAA tiers and the bracket set the room. At your RMD start age (73 for those born 1951–1959, 75 for 1960 and later, per SECURE 2.0), RMDs start taking up bracket space.
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See this in your state
Federal tax brackets and the ACA cliff are uniform, but the dollar damage of crossing it depends on state tax. Top-tax states (worst stack-up) and no-state-tax states (cleanest math):
Each state page has the federal-state-ACA stack-up worked out with a state-specific Roth conversion example, plus the state's 30-year Monte Carlo retirement success rate (from our 51-state research).