Roth Conversion at 64: Your Last Year Before Medicare

At 64, you're one year from Medicare — and you're still operating under the ACA income constraint that has shaped your conversion strategy since you retired. The 400% Federal Poverty Level cliff ($62,600 for single filers, $84,600 for couples) caps your annual conversion just as it did at 62 and 63. Nothing structural has changed in terms of rules.

But strategically, 64 is different from any prior ACA year in one important respect: it's the last one. That changes the calculus in ways that are worth working through explicitly — because decisions you make at 64 have consequences that follow you into Medicare, and you have exactly one year left to optimize within the ACA framework before the rules change entirely at 65.

This guide covers the three planning decisions unique to age 64: the deliberate ACA cliff-crossing analysis (should you accept a one-year penalty for a larger conversion?), the IRMAA delayed-consequence preview (your 64 income determines your age-66 Medicare premiums, not 65), and the end of the SECURE 2.0 super catch-up that applied from 60 through 63.

The ACA constraint still applies — but this is its final year

If you're retired and on ACA Marketplace coverage at 64, Roth conversions count as ordinary income and push your MAGI toward the 400% FPL cliff. Cross $62,600 (single) or $84,600 (couple filing jointly) and you lose your advance premium tax credits entirely — typically $10,000–$25,000 in annual premium support, depending on your plan and location.¹

In prior ACA years, the strategy was straightforward: convert up to just under the cliff, year after year. At 64, that same strategy still works — but now you're deciding whether to apply it one final time or take a different approach for the last year before Medicare.

The reason this matters: at 65, Medicare enrollment ends your ACA eligibility. The cliff disappears. Your conversion ceiling jumps to the IRMAA Tier 1 threshold: $218,000 MAGI for married couples, $109,000 for single filers — two to three times the ACA ceiling. Whatever you couldn't convert in the ACA years can be converted at scale starting at 65.

So the question at 64 is not "how do I stay under the cliff?" It's "what is the mathematically optimal way to handle my last ACA year?"

The deliberate cliff-crossing analysis

Some retirees in their final ACA year choose to accept the cliff penalty deliberately — converting substantially more than the ACA ceiling allows in exchange for moving a large block of traditional IRA money into Roth at low current tax rates. The logic:

• The ACA penalty is a one-time cost. You only pay it for one year (64), not again, because you'll be on Medicare at 65.
• The tax savings from conversion at 22–24% now vs. 32–37% at RMD age are permanent and compound over time.
• A large conversion at 64 shifts your IRMAA consequences to age 66 (not 65), because IRMAA uses a two-year lookback — your 2026 income affects 2028 Medicare premiums.

The tradeoff looks like this for a typical couple:

Illustrative example for a couple with $2M traditional IRA, $15K non-conversion income, and ACA plan with ~$18,000 in annual subsidies. ACA penalty reflects loss of advance premium tax credits. IRMAA cost is for the year income appears in the lookback (age 66), then returns to base rate if conversion is not repeated. 2026 IRMAA thresholds per CMS.

When the cliff-cross makes sense

The deliberate cliff strategy at 64 typically makes sense when all of the following are true:

1. You have a large IRA balance — enough that getting an extra $80,000–$200,000 into Roth materially reduces future RMD exposure.
2. Your ACA subsidies are modest — if your plan is low-cost or your subsidy is small because you live in a competitive insurance market, the penalty for crossing the cliff is lower.
3. You expect significantly higher brackets at RMD age — if RMDs will push you from 22–24% now into 32–37% later, the rate differential justifies a one-year penalty.
4. Your spouse (if applicable) is also turning 65 soon — if both spouses will be on Medicare within the next 1–2 years, the penalty window is short.

When it doesn't make sense

Crossing the cliff is not worth it if your ACA subsidies are large (over $20,000/year), if the rate differential between now and RMD brackets is narrow (both are 22–24%), or if you have limited IRA balance remaining after prior conversions. Run the numbers for your specific situation before accepting the penalty.

The IRMAA two-year lookback: your 64 income sets age-66 premiums

Here's the mechanism that often surprises retirees who deliberately cross the ACA cliff at 64: the IRMAA consequences don't arrive at 65. They arrive at 66.

IRMAA for Medicare Part B and D is based on your MAGI two years prior. If you're 64 in 2026, turning 65 in 2027:

• 2027 IRMAA (age 65) is based on your 2025 income — the year you were 63.
• 2028 IRMAA (age 66) is based on your 2026 income — the year you are 64.

This is counterintuitive but important: a large conversion at 64 doesn't create IRMAA at 65. You get one free year before the surcharge appears. At 65, your Medicare premiums are determined by what you did at 63 — if you stayed under the ACA ceiling then, your first year on Medicare has no IRMAA surcharge.

The IRMAA at 66 is real — it's $2,296/year for a couple crossing Tier 1, or $5,786 crossing Tier 2 — but it's typically a one-year surcharge if income returns to normal in 2027 (age 65). Whether that one-year IRMAA cost is worth the conversion depends on the same rate-differential math above.

For a person turning 64 in 2026. IRMAA uses a two-year lookback. A large conversion at 64 creates a one-year IRMAA surcharge at 66, not at 65.

The end of the super catch-up

If you've been maximizing your 401(k) contributions since age 60, you've had access to the SECURE 2.0 super catch-up: a higher catch-up limit of $11,250 that applies only at ages 60, 61, 62, and 63. At 64, that special limit ends. You revert to the standard 50+ catch-up of $8,000.²

The practical effect:

• At 63: $24,500 + $11,250 = $35,750 total 401(k) deferral // SECURE 2.0 § 109, 2026 IRS limits
• At 64: $24,500 + $8,000 = $32,500 total 401(k) deferral // standard 50+ catch-up

The $3,250 reduction in annual pre-tax contributions means $3,250 more in taxable income if you were previously maxing the 401(k). Depending on your tax situation, you can offset this by:

• Directing the extra $3,250 to after-tax 401(k) contributions (if your plan allows) for potential mega backdoor Roth
• Using the extra taxable income as additional conversion capacity in the 22% bracket
• Increasing HSA contributions if you're on a high-deductible health plan (still on ACA)

Conversion sizing at 64

Most 64-year-olds on ACA face one of two decisions:

Option A — Final ACA discipline (stay under the cliff): Convert $55,000–$70,000 for a couple, same as prior years. Preserve subsidies. Rely on Medicare years starting at 65 for large-scale conversions. This works well if your IRA is manageable relative to the conversion runway ahead, and if ACA subsidies are substantial.

Option B — Deliberate cliff-cross (final opportunity): Accept the one-year ACA penalty and convert $150,000–$250,000. This front-loads Roth conversion in exchange for a one-time cost, taking advantage of the fact that (a) the penalty is never repeated and (b) the IRMAA from this action doesn't hit until 66. Works best with large IRA balances and modest ACA plans.

There's also an Option C: convert just modestly above the cliff — enough to justify the penalty with meaningful conversion volume, but not so much that you push into IRMAA Tier 2 at 66. The $218,000 IRMAA Tier 1 ceiling for MFJ gives substantial room above the $84,600 ACA cliff before the surcharge escalates further.

Worked example: Karen and David, age 64

Karen and David are both 64, retired three years ago, and have been carefully converting under the ACA cliff each year. Their situation in 2026:

• Traditional IRA balance: $1.6M (was $1.9M at retirement; conversions moved $300,000 to Roth)
• Social Security: both delaying to 70 — no SS income yet
• Other income: $12,000/year in dividends
• ACA subsidies: ~$22,000/year (they live in a high-premium market)
• Filing jointly. Both turn 65 in 2027.

Option A analysis: Convert $70,000 ($84,600 ceiling − $12,000 other income − $2,600 buffer). Pay zero ACA penalty. At 65 next year, their IRMAA window opens at $218,000 and they accelerate conversions substantially. This is the conservative path.

Option B analysis: Consider converting $180,000 at 64. Extra ACA cost: ~$22,000 (full subsidy loss). Tax on $180,000 conversion: at 12–22% effective rate, roughly $30,000–$40,000 in federal income tax. IRMAA consequence at 66: $180,000 + $12,000 = $192,000 MAGI — below Tier 1 ($218,000). No IRMAA at all. The only extra cost vs. Option A is the $22,000 ACA penalty.

For Karen and David, Option B is actually viable — the $22,000 penalty converts an extra $110,000 into Roth at 22% instead of the 32% bracket they expect when RMDs begin at 75. That $110,000 generates $11,000/year in tax savings once it starts coming out tax-free. The penalty is recovered in under 2 years of RMD tax savings.

The decision: They elect Option B — convert $180,000 in 2026, accepting the $22,000 ACA penalty. Their 2026 tax bill increases by roughly $24,000 (conversion tax), and they pay full ACA premiums of approximately $22,000 out of pocket. Total extra cost: ~$46,000. In exchange, they move $180,000 into Roth instead of $70,000 — an extra $110,000 that will compound tax-free and reduce future RMDs. Starting at 65, their IRMAA window opens and they convert aggressively for the remaining 10 years before RMDs at 75.

What comes next: the Medicare leap at 65

The at-65 transition is the single biggest structural change in the Roth conversion plan. ACA eligibility ends. The IRMAA-based ceiling opens at $109,000 (single) or $218,000 (MFJ) — far above the ACA cliff. For most couples with large IRAs, the post-Medicare conversion window allows $150,000–$200,000 per year rather than $60,000–$80,000.

If you've been converting $65,000/year for four ACA years at 60–64 (moving $260,000 to Roth), you have a large balance remaining. The 10 years from 65 to 75 (RMD age for those born 1960+) are when the real volume of conversion happens. See the age-65 guide for the full Medicare transition playbook, including the Medigap open enrollment window and how the IRMAA two-year lookback affects your first Medicare years.

Frequently asked questions

Can I do a Roth conversion at 64 if I'm still on ACA?

Yes. There's no rule that prevents Roth conversions while you have ACA coverage. The only consequence is that the conversion increases your MAGI, which can push you above the 400% FPL cliff and eliminate your advance premium tax credits. You must weigh the tax savings from the conversion against the cost of losing the subsidy. Many retirees at 64 deliberately stay under the cliff ceiling; others in their final ACA year accept the one-time penalty to convert more.

Does my Roth conversion at 64 affect my Medicare premiums at 65?

No — it affects your Medicare premiums at 66, not 65. IRMAA uses a two-year lookback. Your 2026 income (age 64) determines your 2028 Medicare premiums (age 66). Your 2027 Medicare premiums (age 65, first year on Medicare) are based on your 2025 income — the year you were 63. If you stayed under the ACA ceiling at 63, your first Medicare year starts with no IRMAA surcharge.

Should I claim Social Security at 64 to fund living expenses so I can convert more?

Generally no. Claiming SS at 64 adds to MAGI and erodes ACA conversion room — you'd be giving back with one hand what you're trying to gain with the other. More importantly, at 64 you're two years short of your full retirement age (67 for those born 1960+) and six years short of maximum SS at 70. The 8%/year delayed credit from 64 to 70 is a guaranteed return that's hard to match. Most fee-only advisors in this niche recommend delaying SS to 70 and using Roth conversion years for income-tax management, not as a source of living expenses.

What's the best Roth conversion strategy for someone with both a pension and a large IRA at 64?

Pension income stacks on top of conversions and compresses your ACA conversion ceiling significantly. A $40,000 annual pension leaves only $22,000–$44,600 of ACA-safe conversion room for a couple before hitting $84,600. This is one case where the deliberate cliff-crossing strategy makes even more sense, since you're already near the ceiling. An advisor who specializes in Roth conversions can model the multi-year conversion schedule alongside your pension income and SS delay decision.

My spouse is 62 and I'm 64. How does that change the strategy?

If you're on the same ACA plan and file jointly, the household ACA ceiling ($84,600) applies to both of you together. When you turn 65, you enroll in Medicare and leave the ACA plan — but your spouse remains on Marketplace coverage until they turn 65. This creates a 2-3 year gap where the household ACA ceiling still binds because of the younger spouse. The cliff doesn't disappear for the household until the second spouse enrolls in Medicare. The at-65 guide covers the transition-year mechanics in detail.

Sources

1. HHS: 2026 Federal Poverty Guidelines — 2026 Federal Poverty Level tables used to calculate ACA 400% FPL thresholds; single-person and two-person household amounts for the 48 contiguous states and D.C.
2. IRS: 401(k) limit increases to $24,500 for 2026 — 2026 employee deferral limit, standard 50+ catch-up ($8,000), and SECURE 2.0 § 109 super catch-up ($11,250 for ages 60–63 only, not applicable at 64+).
3. CMS: 2026 Medicare Parts B and D IRMAA — 2026 IRMAA thresholds ($109,000 single / $218,000 MFJ for Tier 1), based on 2024 MAGI; two-year lookback mechanism.
4. IRS: Retirement Topics — Catch-Up Contributions — SECURE 2.0 § 109 super catch-up ages 60–63; standard catch-up ($8,000) for ages 50–59 and 64+; 2026 limits.

ACA thresholds based on HHS 2026 FPL guidelines. IRMAA figures from CMS 2026 fact sheet. Contribution limits from IRS Notice 2025-67 and Rev. Proc. 2025-32. All values verified June 2026. Individual ACA subsidy amounts vary by marketplace, plan type, and household size.