ACA Subsidy Corridor

Where a pre-Medicare household's income sits relative to marketplace subsidy eligibility — the floor below which coverage shifts to Medicaid, and the ceiling above which premium credits end

How it works

Marketplace premium tax credit eligibility is expressed as a percentage of the Federal Poverty Level (FPL) for the household. Unlike IRMAA, which is a one-sided ceiling, ACA eligibility is bounded on both ends: too much income and the premium credit disappears, too little and the household is Medicaid-eligible and gets no credit at all. Stratum places each pre-65 year's ACA MAGI on that scale and reports the room remaining in either direction. The corridor is positional only — it does not estimate the premium credit in dollars, which additionally requires the benchmark silver plan premium for the client's specific area.

  1. 1. Calculate ACA MAGI

    Determine Modified Adjusted Gross Income for premium tax credit purposes (IRC §36B(d)(2)(B))

    ACA MAGI = AGI + Tax-Exempt Interest + Non-Taxable Social Security Benefits
    Example: AGI $60,000 + Tax-Exempt Interest $2,000 + Non-Taxable Social Security $6,000 = ACA MAGI $68,000. This is NOT the same as IRMAA MAGI, which is AGI + tax-exempt interest only. The Social Security add-back is the critical difference: a household claiming benefits before 65 can sit far above its AGI on the ACA scale.

  2. 2. Determine the Federal Poverty Level

    Look up the FPL for the household size, using the guidelines published the year before the coverage year

    FPL = Base + (Increment × (Household Size − 1))

2025 guidelines (used for 2026 coverage), 48 contiguous states:
Base (1 person): $15,650
Each additional person: $5,500

Alaska and Hawaii use separate, higher schedules.
    Example: Two-person household, 2026 coverage: $15,650 + $5,500 = $21,150

  3. 3. Locate the subsidy floor

    The floor depends on whether the client's state adopted the ACA Medicaid expansion

    Expansion state:     138% FPL (below this → Medicaid-eligible, no premium credit)
Non-expansion state: 100% FPL (below this → the coverage gap: no Medicaid, no credit)
    Example: Two-person household in California (expansion), 2026: Floor = $21,150 × 1.38 = $29,187 Same household in Texas (non-expansion): Floor = $21,150 × 1.00 = $21,150

  4. 4. Locate the cost-sharing steps and the cliff

    Within the corridor, silver plan cost-sharing improves at lower incomes; above the cliff the credit ends

    150% FPL — top of the 94% actuarial value tier
200% FPL — top of the 87% tier
250% FPL — top of the 73% tier
400% FPL — the subsidy cliff (45 CFR §155.305(g); IRC §36B(c)(1)(A))
    Example: Two-person household, 2026, expansion state: 138% floor: $29,187 150%: $31,725 200%: $42,300 250%: $52,875 400% cliff: $84,600

  5. 5. Report position and headroom

    Place ACA MAGI on the corridor and measure the distance to the nearest binding constraint

    % FPL = ACA MAGI ÷ FPL
Headroom to cliff = Cliff Amount − ACA MAGI
Cushion above floor = ACA MAGI − Floor Amount
    Example: ACA MAGI $60,000 ÷ FPL $21,150 = 284% FPL Headroom to cliff: $84,600 − $60,000 = $24,600 A Roth conversion above $24,600 in this year would cross the cliff and end the premium credit entirely.

Real-world context

Why the corridor matters most between 55 and 65

The years between early retirement and Medicare are exactly when a household has the most control over its taxable income — and exactly when marketplace subsidies are in play. This is the same window in which Roth conversions are most attractive. The two goals are in direct tension: every dollar converted raises ACA MAGI, and crossing the cliff can cost more than the conversion saves. At 65 the constraint hands off to IRMAA, which has its own two-year lookback.

IRS reference: IRC §36B

The floor is not a safety net

Falling below the subsidy floor is not a good outcome for most planning clients. In expansion states, adults below 138% FPL qualify for Medicaid based on income alone — there is no asset test for this category. A retiree with substantial assets and low realized income is Medicaid-eligible, which makes them ineligible for a premium tax credit. Clients living off Roth distributions and taxable-account basis can land here without realizing it. The fix is often to deliberately create income — a modest Roth conversion or gain harvest — to climb above the floor.

IRS reference: 42 U.S.C. §1396a(a)(10)(A)(i)(VIII)

The coverage gap in non-expansion states

In states that did not adopt the Medicaid expansion, income below 100% FPL falls into the coverage gap: too low for a premium tax credit, too high for Medicaid under the state's narrower rules. This is materially worse than the expansion-state floor. Wisconsin is the exception among non-expansion states — it covers adults to 100% FPL under a waiver, so there is no gap there.

The phase-out is a hidden surtax

Even well below the cliff, the premium credit shrinks as income rises. Across the middle FPL bands that phase-out behaves like an additional 10 to 15 percentage points of marginal tax on top of the statutory bracket. A client who appears to be in the 12% bracket may face a true marginal cost closer to 25%. At the cliff itself, a single dollar of additional income can cost the entire annual credit.

IRS reference: IRC §36B(b)(3)(A)

Basis is the lever

Because ACA MAGI counts only the taxable portion of a withdrawal, funding living expenses from a taxable account with high basis generates far less ACA MAGI than an equivalent draw from a tax-deferred account. A $90,000 spending need met from a taxable account at 20% basis ratio produces a fraction of the MAGI that a $90,000 IRA distribution would. This is frequently the difference between staying in the corridor and losing the credit.

What drives the result

Filing Status
Assumptions → Filing Status

Sets the Federal Poverty Level denominator, which scales every boundary on the corridor. Married filing jointly gives a two-person household; everything else gives one. There is no separate household size field. A survivor year follows the resolved filing status automatically, dropping the household to one.

Two-person household, 2026: FPL $21,150, cliff at $84,600 One-person household, 2026: FPL $15,650, cliff at $62,600

Medicaid expansion state
Assumptions → State Assumptions

Determines whether the subsidy floor sits at 138% or 100% FPL, and whether income below the floor routes to Medicaid or into the coverage gap. Set automatically from the state profile when a state is picked; override when the client's situation differs. Shown regardless of the state income tax rate, since several non-expansion states have no income tax.

Two-person household, 2026: Expansion state floor: $29,187 Non-expansion state floor: $21,150

400% FPL ACA subsidy cliff applies
Assumptions → Federal Tax Environment

When on, the premium credit ends entirely above 400% FPL and the corridor has a hard ceiling. When off, the credit phases out gradually with the household contribution capped at 8.5% of income, and there is no upper wall — only the cost-sharing steps below. Grouped with the federal rate shift because it is a question about future law rather than a client fact.

Cliff on: income above $84,600 shows as outside the corridor Cliff off: income above $84,600 remains subsidized, at a declining rate

Roth Conversion Amount
Roth Conversion Strategy

Conversion income raises ACA MAGI dollar for dollar in the conversion year. In a pre-Medicare year this can consume the headroom to the cliff and end the premium credit. Compare the headroom figure on the Federal Tax Analysis tab against the planned conversion before committing to it.

ACA MAGI $60,000, headroom to cliff $24,600 Converting $40,000 crosses the cliff; converting $24,000 does not

State
Assumptions → State Assumptions

Sets the default Medicaid expansion status and selects the FPL schedule. Alaska and Hawaii use their own, higher poverty guidelines.

One-person household, 2026 coverage: 48 states: FPL $15,650 Alaska: FPL $19,550 Hawaii: FPL $17,990

Assumptions

  • ACA MAGI = AGI + tax-exempt interest + the portion of Social Security excluded from gross income (IRC §36B(d)(2)(B))
  • Household size is derived from filing status — two for married filing jointly, one otherwise — and is not entered separately
  • The FPL guidelines for a coverage year are those published the prior calendar year, matching marketplace eligibility determination
  • FPL figures beyond the latest published HHS table are indexed forward at the scenario inflation rate
  • Medicaid expansion status is derived from the scenario's state and can be overridden
  • The 400% FPL cliff is treated as active by default; it can be switched off per scenario
  • The corridor applies only to years in which at least one living household member is below age 65
  • A survivor year automatically drops the household to one person, following the resolved filing status

Limitations

  • Does not estimate the premium tax credit in dollars — that requires the Second Lowest Cost Silver Plan benchmark premium for the client's county and the ages of everyone covered
  • Does not model dependents individually. Age-outs, disability provisions, and custody arrangements are not tracked, and household size comes from filing status alone — a household covering dependents on its marketplace plan will show a higher % FPL than it should
  • Does not model the foreign earned income exclusion add-back (rare for the pre-Medicare retiree population)
  • Does not model repayment caps on excess advance premium tax credits, which are themselves FPL-banded
  • Does not distinguish between household members who are on marketplace coverage and those covered elsewhere (employer, Medicare, VA) — the FPL denominator is the tax household
  • Treatment of the 400% cliff has been subject to temporary legislation; the default reflects the statutory structure and should be reviewed against current law

Related

This page explains how Stratum models this calculation. It is educational material for financial professionals, not tax or legal advice, and tax law changes. Verify current figures against primary IRS sources before relying on them with a client.