Roth Conversion at 65: Medicare Changes Everything

For early retirees doing Roth conversions during ACA years, age 65 feels like a finish line. The ACA income ceiling that capped your annual conversion at $62,600 (single) or $84,600 (couple) disappears. Medicare doesn't care how much you earn — it charges flat premiums, with income surcharges only above thresholds far higher than the ACA cliff. For a married couple delaying Social Security, that typically means a conversion ceiling of $180,000–$200,000 per year: two to three times what ACA allowed.

But age 65 brings its own complexity. The IRMAA two-year lookback means your age-63 conversions are already priced into your first Medicare premiums. The Medigap open enrollment window opens the moment you enroll in Part B — and closes six months later, permanently. And the size of your new conversion ceiling depends on whether you've claimed Social Security, how much you hold in taxable accounts, and how aggressively you converted in the final ACA years.

This guide covers the full 65-year transition: what changes, what carries forward, and how to size conversions in the first years of Medicare.

What actually changes at 65

The ACA income constraint ends

From the time you retired until Medicare enrollment, Roth conversions pushed your Modified Adjusted Gross Income — and MAGI above the 400% Federal Poverty Level threshold eliminated your advance premium tax credits in full. That cliff constrained most early retirees to $50,000–$80,000 in annual conversions.

At 65, Medicare enrollment ends ACA Marketplace eligibility. Medicare premiums are not income-linked at the base level — all enrollees pay the same $202.90/month Part B base premium regardless of income.¹ Income surcharges (IRMAA) only apply above $109,000 MAGI for single filers or $218,000 for married couples filing jointly. For most retirees delaying Social Security, these thresholds are far above what they previously had room to convert.

IRMAA replaces the ACA cliff — at a much higher floor

IRMAA surcharges work differently from the ACA cliff. The ACA cliff was binary: cross $84,600 and lose the entire subsidy. IRMAA is tiered — cross a threshold and pay a surcharge per person per month, but only on the amount in that tier. And the thresholds start much higher:

2026 IRMAA thresholds based on 2024 MAGI. Source: CMS 2026 Medicare Part B and D premium data. Part D surcharge depends on your plan; amounts shown are standard IRMAA surcharges.

A married couple with no Social Security, $20,000 in dividends, and no other income can convert up to $197,999 before crossing into IRMAA Tier 1 — and even after crossing, the surcharge is $1,148/person/year ($2,296 for a couple), not a cliff.

The Medigap open enrollment window opens

When you first enroll in Medicare Part B and you're 65 or older, federal law grants you a six-month Medigap open enrollment period.² During this window, any Medicare supplement insurer operating in your state must sell you any Medigap plan they offer — at standard rates, regardless of your health history or pre-existing conditions.

After this window closes, insurers in most states can use medical underwriting. A retired 65-year-old with a history of cancer, diabetes, or heart disease who tries to buy Medigap outside the open enrollment window may be denied or charged substantially higher rates.

The window doesn't affect Roth conversions directly. But it matters for the sequencing of Medicare decisions: you should not delay Medigap enrollment to optimize a conversion. Get the Medigap policy in place during the guaranteed window, and plan conversions around the IRMAA tiers above — not around Medigap premiums, which are the same regardless of income.

The IRMAA two-year lookback: what your conversions at 63 already set

Here's the mechanism most people miss: IRMAA for 2026 is based on your 2024 MAGI — two years earlier. So the moment you enroll in Medicare at 65, your first year's premiums are already determined by what you did at 63.

This creates a specific planning problem for retirees who deliberately crossed the ACA cliff in their last Marketplace year. Consider a couple who converted aggressively in 2024 at age 63 — accepting a one-year ACA penalty to move $180,000 out of a large IRA. That $180,000 conversion pushed their 2024 MAGI above $218,000, directly into IRMAA Tier 1 for their 2026 Medicare premiums. The ACA penalty was a one-time cost; the IRMAA surcharge follows them into Medicare.

Whether that tradeoff made sense depends on the specific numbers — but the point is that you can't plan age-65 conversions in isolation from age-63 decisions. The lookback connects them.

What the lookback means going forward

Conversions you do at 65 set your premiums at 67. Conversions at 66 set premiums at 68. This creates a two-year delay between actions and consequences — and a two-year window to manage future premium exposure. An unusually large conversion in 2026 (age 65) triggers a one-year IRMAA surcharge in 2028 (age 67). If your income returns to base rate in 2027, the 2029 premium drops back. The SSA-44 appeal process also allows retirees to request a reduction if income dropped significantly after a life-changing event.

Social Security coordination at 65

Most fee-only advisors recommend delaying Social Security until 70 for the highest-earning spouse — locking in an 8%/year delayed credit plus inflation adjustments. If neither spouse has claimed SS at 65, conversion calculations are simpler: the conversion itself is nearly all of your MAGI.

But some people claim SS at 65 (at their full retirement age if born before 1960, or slightly before FRA if born 1960+, where FRA is 67). SS income stacks on top of conversions and raises your MAGI. The Social Security and Roth conversion guide covers the combined income formula and the 1.5×–1.85× effective rate multipliers in SS phase-in zones. In brief:

• If you're single and claiming SS at 65, the first ~$34,000 of combined income triggers the 50% taxable phase-in — each dollar of conversion can add $1.50 in taxable income due to the SS torpedo.
• Delaying SS to 70 while converting at 65–69 is a common strategy: no SS to erode conversion space, and Roth money will supplement income after SS starts.

Sizing conversions in the first years of Medicare

The jump from ACA conversion ceiling to IRMAA-floor conversion ceiling is substantial. Here's how to think about sizing conversions in the first Medicare years:

Step 1: Establish your non-conversion income baseline

List all income sources that will count in MAGI regardless of whether you convert: dividends, interest, capital gains distributions from taxable accounts, rental income, pension payments, any SS benefits you've claimed. This is your floor before the first dollar of conversion.

Step 2: Set your conversion target bracket

Most retirees in their late 60s with large IRAs and no Social Security can convert to the top of the 22% or 24% federal bracket without crossing IRMAA Tier 1. The 2026 MFJ 22% bracket tops out at $201,050 in taxable income; the 24% bracket tops at $383,900. For single filers, the 22% bracket runs through $100,525 and the 24% through $191,950.³

With no SS and modest passive income, many couples can convert $150,000–$180,000/year while staying below $218,000 MAGI (IRMAA Tier 1 for MFJ) — roughly three to four times what they could convert during ACA years.

Step 3: Decide whether crossing into IRMAA Tier 1 makes sense

Tier 1 IRMAA is $1,148/year per person — $2,296 for a couple. If crossing into Tier 1 allows you to convert an extra $30,000–$50,000 at 22% now rather than 32% later (when RMDs hit), the annual IRMAA cost is typically recovered in the first year or two of tax savings. The IRMAA guide includes the full break-even analysis.

Worked example: Barbara and Jim turn 65

Barbara (65) and Jim (64) both retired at 62. They spent three years on ACA Marketplace coverage, carefully keeping MAGI below $84,600/year while converting $55,000–$70,000 annually. Barbara turns 65 in January 2026 and enrolls in Medicare Part B and Part D. Jim remains on ACA until he turns 65 in 2027.

Their situation:

• Traditional IRA balance: $1.9M (was $2.1M at retirement; ACA conversions moved $200,000 to Roth)
• Social Security: both delaying to 70 — no SS income yet
• Other income: $18,000/year in dividends and interest
• Filing jointly. Jim still on ACA with a $84,600 ceiling.

IRMAA lookback check: Their 2024 MAGI was $83,500 (just under the ACA ceiling). Barbara's 2026 Medicare premiums are at base rate: $202.90/month, no IRMAA surcharge. Clean start.

2026 conversion plan: Barbara is on Medicare, Jim is still on ACA. They cannot file separately and keep ACA subsidy eligibility for Jim, so their MFJ MAGI ceiling is effectively Jim's ACA ceiling: $84,600. They convert $64,000 — staying under the ACA cliff while Jim is still on Marketplace coverage. This is the same approach as prior ACA years.

2027 and beyond: Jim turns 65 in 2027. Both are now on Medicare. Their new joint ceiling jumps dramatically:

• Non-conversion MAGI: $18,000 (dividends/interest)
• IRMAA Tier 1 threshold (MFJ): $218,000
• Available conversion room: $218,000 − $18,000 = $200,000

They elect to convert $195,000 in 2027, staying just below Tier 1. Their 2029 IRMAA (based on 2027 MAGI of $213,000) remains at base rate. RMDs don't start until 2035 (Jim born 1962, RMD age 75). From 2027 to 2034 they convert ~$195,000/year — potentially moving $1.5M into Roth and dramatically compressing future RMDs before they begin.

The transition year: one spouse on Medicare, one on ACA

When spouses have different birth years, there's typically a gap where one is on Medicare and one remains on ACA. As in Barbara and Jim's case above, the ACA ceiling applies to the household as long as one spouse remains on Marketplace coverage and you file jointly. The ACA income constraint doesn't lift until both spouses are on Medicare.

In the transition year, strategies include:

• Converting the maximum allowed under the ACA ceiling (as in prior years), since nothing has structurally changed yet
• Considering whether the Medicare-enrolled spouse should file separately — but MFS disqualifies most ACA credits and creates its own problems
• Front-loading conversion in January of the year the second spouse turns 65, once ACA ends mid-year (though partial-year ACA coverage creates pro-rated ceiling calculations)

The cleanest approach is usually to continue ACA-era conversion discipline until both spouses are on Medicare, then step up aggressively in year one of dual Medicare coverage.

Frequently asked questions

Does converting to Roth increase my Medicare premiums?

It can, via IRMAA. Medicare Part B base premiums ($202.90/month in 2026) are flat regardless of income. IRMAA surcharges apply above $109,000 MAGI for single filers or $218,000 for MFJ. The surcharges are tiered and per-person — not a cliff. Because IRMAA is based on income two years prior, conversions you do today affect Medicare premiums two years from now. For most retirees, the tax savings from conversion significantly outweigh IRMAA costs.

What is the IRMAA lookback period?

Two years. Medicare Part B and D premiums for 2026 are based on your 2024 MAGI as reported to the IRS. The SSA uses this information to determine your premium tier. If your income in 2024 was elevated due to a large Roth conversion or a one-time income event, your 2026 Medicare premiums reflect that. If your income dropped significantly since then (due to retirement, reduced income, or another life-changing event), you can appeal via SSA Form SSA-44 to use a more recent year's income.

When does the Medigap open enrollment period start?

The Medigap Open Enrollment Period begins the first day of the month in which you're both 65 or older AND enrolled in Medicare Part B. It lasts six months. During this window, Medigap insurers must accept you at standard rates regardless of pre-existing conditions. This is a one-time federal guarantee — once it closes, insurers in most states can medically underwrite. It has nothing to do with income or Roth conversions, but the timing matters: don't delay Part B enrollment to optimize conversions and accidentally let this window lapse.

Should I convert more aggressively now that I'm on Medicare?

Probably yes — for most retirees with substantial traditional IRA balances. The ACA ceiling (typically $62,600–$84,600/year) was constraining. IRMAA Tier 1 starts at $109,000 (single) or $218,000 (MFJ). If you've been converting $60,000/year on ACA, you may be able to convert $150,000–$200,000/year on Medicare — completing significantly more of the IRA balance before RMDs force distributions at potentially higher brackets. The RMD reduction guide and lifetime NPV calculator can quantify the benefit for your specific balance.

Can I appeal IRMAA if my income dropped after the lookback year?

Yes. If you experienced a life-changing event (retirement, reduced work hours, divorce, death of a spouse, loss of income-producing property, or reduction of pension income), you can file SSA Form SSA-44 to request Medicare use a more recent year's income. Standard qualifying events are clearly defined by the SSA. A Roth conversion in the lookback year that was a one-time event doesn't typically qualify as a "life-changing event" for SSA-44 purposes — the event must be ongoing income reduction, not a past investment decision.

I'm turning 65 mid-year. How do the ACA and Medicare interact?

Medicare eligibility begins the first day of your birth month (or three months earlier if you're applying for delayed Part B). Once enrolled in Medicare, you're no longer eligible for ACA Marketplace coverage — the two programs don't overlap. Your ACA plan terminates when Medicare begins. For the months you were on ACA, the usual ceiling math applies. After Medicare enrollment, IRMAA-based conversion math takes over. For the year as a whole, your total MAGI includes both periods — worth coordinating with an advisor in the transition year to avoid inadvertently crossing the ACA cliff in the months before Medicare starts.

The bigger picture: years 65–75

For most people born in 1960 or later, RMDs don't begin until 75 (SECURE 2.0, § 107). That creates up to a ten-year window after Medicare enrollment — and possibly fifteen or more years after retirement — to convert traditional IRA balances at controlled tax rates.

The jump from ACA ceilings to IRMAA-floor conversion room is often the biggest single acceleration point in the Roth conversion plan. Retirees who spent ten ACA years converting $60,000–$80,000/year may be able to finish the same amount in three or four Medicare years — if they start immediately and convert aggressively in the IRMAA-safe window.

Use the lifetime NPV calculator to model your specific scenario: pre-RMD balance, RMD start year, expected post-RMD bracket, and conversion pace. For the IRA-to-Roth math at scale — including IRMAA coordination, Social Security timing, and state tax — a fee-only advisor who specializes in this kind of multi-year modeling is likely to surface opportunities that a spreadsheet misses.

Sources

1. CMS: 2026 Medicare Parts B and D Income-Related Monthly Adjustment Amounts — 2026 IRMAA tier thresholds, Part B and Part D surcharge amounts, and base premium of $202.90/month. Based on 2024 MAGI (two-year lookback).
2. Medicare.gov: When Can I Buy Medigap? — description of the Medigap Open Enrollment Period: six months beginning the first month you are 65 or older and enrolled in Medicare Part B; guaranteed issue rights and standard pricing apply during this period only.
3. IRS: Tax Inflation Adjustments for Tax Year 2026 (Rev. Proc. 2025-32) — 2026 federal income tax bracket thresholds for single and married filing jointly filers; standard deduction amounts.
4. SSA: Medicare IRMAA — SSA's administration of IRMAA determinations, appeals process, SSA-44 form for life-changing event reconsideration, and income source used for lookback calculations.

IRMAA thresholds based on CMS 2026 fact sheet. Tax brackets from IRS Rev. Proc. 2025-32. Medigap enrollment rules per federal law (42 U.S.C. § 1395ss). All values verified May 2026. Individual Medicare premium amounts may differ if enrolled in a Medicare Advantage plan.