TL;DR
- Your annual Roth conversion target is the lowest of four ceilings: the 12% tax bracket, the ACA subsidy cliff, the IRMAA brackets (if 63 or older), and your remaining traditional balance.
- For most pre-Medicare early retirees, the ACA cliff is the binding constraint, not the tax bracket. The 2026 cliff for a 2-person household is roughly $81,760 in MAGI, which sits below the $100,800 top of the 12% bracket for joint filers.
- The lowest-tax years of your entire life sit between early retirement and Social Security. Convert aggressively in that window, then taper as RMDs and benefits stack up.
The One-Sentence Formula
The optimal Roth conversion amount in any given year is whatever fills your tax bracket of choice without breaking a separate income-based threshold that costs more than the tax savings.
Most articles stop there and let you figure out the rest. Let's do the actual work.
The four ceilings that determine your conversion size:
- Tax bracket ceiling. How much room exists between your other taxable income and the top of the 12% federal bracket (or whatever rate you've committed to paying).
- ACA subsidy cliff. Your MAGI ceiling before premium tax credits collapse. Pre-Medicare only.
- IRMAA bracket. The income threshold that triggers a Medicare Part B and D premium surcharge. Looks back two years.
- Traditional balance. You can only convert what you have. RMDs at age 73 force the issue if you wait too long.
Your conversion target is the smallest of these four numbers minus your existing taxable income.
Ceiling 1: The 12% Tax Bracket
For 2026, the federal tax brackets and standard deduction look like this:
| Item | Single | Married Filing Jointly |
|---|---|---|
| Standard Deduction | $16,100 | $32,200 |
| Top of 10% Bracket (taxable) | $12,400 | $24,800 |
| Top of 12% Bracket (taxable) | $50,400 | $100,800 |
| Top of 12% Bracket (gross income, after std deduction) | $66,500 | $133,000 |
| Top of 22% Bracket (taxable) | $105,700 | $211,400 |
To find your conversion ceiling for the 12% bracket, take the gross-income figure and subtract any income you already expect (interest, dividends, part-time work, pension, taxable Social Security). What's left is the largest conversion that keeps every dollar in the 12% bracket or lower.
For deeper detail on this layering, see the exact 2026 dollar amounts for filling the 12% bracket.
Ceiling 2: The ACA Subsidy Cliff
If you're under 65 and rely on the Affordable Care Act marketplace for health insurance, your premium tax credits depend on your MAGI staying inside Federal Poverty Level (FPL) bands. For 2026, the relevant cliff sits at 400% of FPL based on the 2025 FPL figures used for 2026 plan year calculations.
| Household Size | 100% FPL (2025) | 400% FPL (Subsidy Cliff) |
|---|---|---|
| 1 person | $15,650 | $62,600 |
| 2 people | $21,150 | $84,600 |
| 3 people | $26,650 | $106,600 |
| 4 people | $32,150 | $128,600 |
Cliff vs phaseout: The original ACA had a hard cliff at 400% FPL. The American Rescue Plan and Inflation Reduction Act softened this through 2025, capping premiums at 8.5% of MAGI. As of 2026 these enhanced subsidies have expired. Confirm the current rules with healthcare.gov before relying on this in your plan.
For most 2-person households retired before Medicare age, the ACA cliff is the binding constraint. You can technically convert more and pay 12% federal tax, but the marginal cost of losing the subsidy can exceed $10,000 per year. The full math is in the ACA subsidy cliff explained.
Ceiling 3: IRMAA (Ages 63 and Up)
IRMAA stands for Income-Related Monthly Adjustment Amount. It's a Medicare premium surcharge that kicks in when your MAGI from two years prior exceeds certain thresholds. So your 2026 income directly affects your 2028 Medicare premiums. If you'll be 65 or older in 2028, you need to manage this now.
For 2026 (based on 2024 income), the first IRMAA tier starts above $109,000 single or $218,000 MFJ. The Part B surcharge is $81.20 per month, plus a Part D surcharge of $14.50, for $95.70 per person per month. A couple crossing that tier pays roughly $2,297 extra annually for the rest of their lives in Medicare. Higher tiers get progressively worse. The IRMAA tables shift each year with inflation, but the design rarely changes.
At ages 63 and 64, every dollar of income converted shows up in the IRMAA lookback. This is the most overlooked Roth conversion constraint and the one that surprises people most.
Ceiling 4: Your Traditional Balance
You can only convert what's in a traditional IRA, traditional 401(k), or similar pre-tax account. Roth 401(k) money isn't a conversion candidate, it's already Roth. After-tax brokerage isn't either.
If you have $400,000 in a traditional IRA at age 50 and plan to retire at 55, you have roughly 18 years before RMDs begin at age 73. That's 18 conversion windows. If you spread $400,000 over 18 years (ignoring growth), you'd convert about $22,200 per year. Add growth and the actual amount needed to deplete the traditional account before RMDs is much higher, often double or triple that.
This is why the math matters. Underconverting leaves a giant traditional balance to be force-distributed at RMD age, often pushing you back into the 22% or 24% bracket and triggering IRMAA. Overconverting wastes ACA subsidies and possibly triggers IRMAA in your final pre-Medicare years. The sweet spot lives between these failure modes.
Worked Example 1: No Other Income, MFJ, Age 52
Married couple, both 52, just retired. ACA marketplace, household of 2. Bank interest is small (under $500). Goal: convert as much as possible while keeping ACA subsidies.
| Constraint | Ceiling | Other Income | Conversion Room |
|---|---|---|---|
| 12% Bracket (gross) | $133,000 | $500 | $127,950 |
| ACA 400% FPL (2 people) | $84,600 | $500 | $84,100 |
| IRMAA (not yet age 63) | n/a | n/a | n/a |
| Binding constraint | ACA | $84,100 |
This couple converts about $84,000 per year, paying around $5,800 in federal tax (mostly at 10% and 12%) and preserving thousands in ACA subsidies. The federal effective rate on the conversion is roughly 6.9%.
Worked Example 2: Pension, MFJ, Age 60
Married couple. One retired with a $42,000 annual pension. Both on ACA marketplace. Household of 2. They want to keep converting before Medicare hits.
| Constraint | Ceiling | Other Income | Conversion Room |
|---|---|---|---|
| 12% Bracket (gross) | $133,000 | $42,000 | $91,000 |
| ACA 400% FPL (2 people) | $84,600 | $42,000 | $42,600 |
| IRMAA lookback (62 + 2 = 64, partly relevant) | $218,000 | $42,000 | $176,000 |
| Binding constraint | ACA | $42,600 |
Half the conversion room of Example 1, because the pension already eats into the ACA cap. Notice that by age 63 the IRMAA constraint becomes meaningful, but it's still slack here.
Worked Example 3: Both on Medicare, MFJ, Age 67
Married couple, both 67. ACA constraint gone. Both took Social Security at 67: $36,000 each ($72,000 total benefits, of which 85% or $61,200 is taxable). Pension of $24,000. Aiming for a conversion strategy that doesn't break IRMAA.
| Constraint | Ceiling | Other Income | Conversion Room |
|---|---|---|---|
| 12% Bracket (gross) | $133,000 | $85,200 (pension + taxable SS) | $47,800 |
| IRMAA Tier 1 (MFJ) | $218,000 | $85,200 | $132,800 |
| 22% Bracket (gross) | $243,600 | $85,200 | $153,000 |
| Binding constraint | 12% bracket | $47,800 |
Once Social Security and Medicare are active, the math flips. The 12% bracket becomes the binding line for most retirees, not the ACA cliff. Conversion sizes shrink because Social Security has eaten into the bracket. This is exactly why the early-retirement window matters so much.
Run Your Annual Conversion Numbers
Plug your accounts, ages, and household details into the calculator and see your conversion ceiling for every year of retirement.
Open BridgeToFI Calculator →The "Convert More Now or Less Later" Question
You'll often hear early retirees ask whether they should convert aggressively (filling the 12% bracket every year) or conservatively (just enough to deplete the traditional balance by age 95). The right answer depends on three forecasts:
- Future tax rates. If you expect rates to rise (Tax Cuts and Jobs Act sunset, deficit pressure, demographic changes), convert more now.
- Investment returns. Higher expected returns favor aggressive conversion because the traditional balance grows faster than you can shrink it.
- Charitable intent. If you plan large Qualified Charitable Distributions in your 70s, you don't need to fully drain the traditional account. QCDs come from traditional IRAs and don't count as taxable income.
The honest take: For most early retirees with no charitable plans, convert aggressively in your low-income years (retirement to age 62), moderately during the IRMAA-sensitive window (63 to 65), then opportunistically once you're on Medicare. By age 75 your traditional balance should be small enough that RMDs don't push you into a higher bracket.
Common Mistakes That Destroy the Math
1. Converting in December without checking year-to-date income
December conversions feel safe because tax season is around the corner. But by December, you've already received any 1099 income, K-1 distributions, capital gain distributions from mutual funds, and dividend income. Add a too-large conversion on top and you discover you're in the 22% bracket on the last $4,200 of conversion in February. Run the math in November, leave a $5,000 buffer, then commit in mid-December.
2. Forgetting state taxes
Federal tax is one layer. Most states tax Roth conversions as ordinary income (a few don't tax retirement income at all, see California for the worst case at 9.3% on top of federal). If you're in a 5% state, your "12% federal bracket" Roth conversion actually costs 17% all-in. The strategy still works in most states but the threshold for "is this worth it" shifts.
3. Using last year's bracket numbers
The 2026 figures above are different from 2025, which were different from 2024. The standard deduction, bracket thresholds, FPL numbers, and IRMAA bands all index to inflation. Always use the current year's table when calculating, not the one your accountant printed last spring.
4. Ignoring net investment income tax (NIIT)
The 3.8% Net Investment Income Tax applies to investment income above $200,000 single or $250,000 MFJ. Roth conversions themselves aren't subject to NIIT, but they raise your MAGI and can push your investment income across the threshold. For most early retirees this is not an issue, but if you have a large taxable brokerage throwing off six-figure capital gains, it's worth checking.
What If You Have Too Much Traditional Money?
Some retirees discover at age 60 that the math doesn't work. Their traditional balance is so large that even maxing the 12% bracket every year for 13 years won't drain it before RMDs kick in.
If that's you, the choice is:
- Accept the 22% bracket. Convert into the 22% bracket selectively. The 12% to 22% gap is the worst place to live. The 22% to 24% gap is much smaller. Many retirees rationally pay 22% on conversions to avoid 24% or higher RMDs later.
- Sacrifice ACA subsidies. If you have a few years before Medicare, give up the subsidy and convert all the way to the top of the 12% bracket. Sometimes the math works.
- Plan for QCDs. Starting at age 70.5, you can give up to $108,000 (2025 figure, indexes to inflation) per year directly from a traditional IRA to charity. This doesn't count as income and reduces your future RMD base. If you're charitably inclined, factor this in.
The Annual Checklist
Run through this in October or November of each year:
- Pull a year-to-date income summary from your brokerage and bank.
- Look up the current year's tax brackets, FPL numbers, and IRMAA bands.
- Calculate the four ceilings. The smallest one is your binding constraint.
- Subtract a 5-10% safety buffer for unexpected income.
- Submit the conversion in mid-December once W-2 employees have received their final paystubs and most year-end distributions are visible.
- Pay the estimated tax with a Q4 estimated payment, not from the converted Roth (paying tax with Roth dollars defeats the purpose).
Key Takeaways
1. There is no single optimal Roth conversion amount. There are four ceilings (tax bracket, ACA, IRMAA, traditional balance) and your target is the smallest binding constraint.
2. For most pre-Medicare early retirees, the ACA cliff binds before the 12% bracket does. Recheck this every year because both numbers move.
3. The years between early retirement and Social Security are the lowest-income years of your life. Convert aggressively then. After Social Security starts, convert smaller amounts within bracket limits.
4. Always pay the conversion tax from a taxable account, never from the converted Roth. Always leave a 5-10% buffer below your ceiling for surprises.
Frequently Asked Questions
What is the optimal Roth conversion amount per year?
There is no universal answer. Most early retirees should convert just enough to fill the 12% federal tax bracket without crossing the ACA subsidy cliff. For 2026 that ceiling is $100,800 in taxable income for joint filers, but the ACA cliff (around $84,600 for a 2-person household) is usually the binding constraint before age 65.
Should I convert more in years before Social Security starts?
Yes, generally. The years between early retirement and your first Social Security check are the lowest-income years of your life. Once Social Security starts, up to 85% of those benefits become taxable income that uses up bracket space. Frontloading conversions in the gap years preserves more low-bracket room than spreading them across your whole retirement.
Can a Roth conversion push me into a higher tax bracket?
Yes, and it's the most common mistake. Only the dollars above the bracket threshold get taxed at the higher rate, but the marginal rate jumps. A conversion crossing from 12% to 22% almost doubles the tax on those dollars. Always run the math before converting and stop a few thousand below the threshold to leave room for unexpected income like 1099 interest or capital gain distributions.