ACA MAGI management: turning the income dial on purpose

By Tom, CPA · Updated October 25, 2026

TL;DR: ACA subsidies are based on MAGI: AGI plus tax-exempt interest, untaxed Social Security and excluded foreign income. Early retirees can steer MAGI with spending order, gain timing, Roth conversions and HSA contributions, then update the marketplace when plans change.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

MAGI is the dial; your subsidy is the volume knob. Turn the dial up and the knob turns down. While you were working, the dial was glued in place by your paycheck. In early retirement it comes unglued, and suddenly you decide how much income you have each year by choosing what to sell, what to convert and what to leave alone.

That is a superpower with a very specific failure mode: people forget which income counts. The marketplace version of MAGI is not the same as the one used for Roth IRA contributions or Medicare IRMAA, and it includes items most people assume are invisible. This guide covers what goes in, what stays out, the levers that move it, and how to estimate it without a crystal ball.

CPA Warning Label: Municipal bond interest is tax-free for income tax and fully visible to the marketplace. Tax-free is not invisible.

What counts in ACA MAGI

HealthCare.gov describes the calculation in three steps: start with adjusted gross income (Form 1040, line 11), add three specific items, then adjust for expected changes during the coverage year.

• Start: AGI. Wages, self-employment profit, taxable interest and dividends, capital gains, taxable IRA and 401(k) distributions, taxable Roth conversions, rental profit, taxable Social Security and pensions, minus above-the-line adjustments.
• Add: tax-exempt interest. Municipal bond interest is excluded from tax but included here.
• Add: non-taxable Social Security. All of your Social Security benefits effectively count, not just the taxable part.
• Add: excluded foreign earned income. Relevant for expats who use the foreign earned income exclusion.
• Don't add: SSI. Supplemental Security Income is not counted.

Household MAGI includes you, your spouse and any tax dependents who are required to file a return, even if they don't need coverage.

What usually does not count: Roth IRA contributions you withdraw, qualified Roth distributions, the principal (basis) portion of a stock sale, loans, gifts you receive, and HSA distributions used for qualified medical expenses.

Tax-exempt interest and Social Security: the stowaways

Two items routinely blindside people.

Municipal bonds. A household that shifted its bond allocation into munis to save tax may discover the marketplace counts every dollar of that interest. A $400,000 muni ladder yielding 3% adds $12,000 to MAGI. For a couple near the cliff, a taxable bond fund held in an IRA may serve the subsidy better than munis in a taxable account.

Social Security. If one spouse claims early while the other is still under 65, the full benefit flows into household MAGI. A $24,000 benefit can eat a third of a couple's room under the 400% line. That is one reason couples with a big age gap often revisit claiming timing.

The levers: conversions, gains, HSA and more

1. Spending order

Living expenses can come from cash, from the basis portion of taxable investments, from Roth contributions, or from pre-tax accounts. Only the last one is fully MAGI. A household with $300,000 of taxable investments at 50% basis can fund $60,000 of spending by selling $60,000 of shares and reporting only $30,000 of gain.

2. Capital gains timing

Selecting specific lots lets you choose high-basis shares in tight years and low-basis shares in roomy years. Loss harvesting can offset gains; up to $3,000 of net capital loss can also reduce other income each year.

3. Roth conversions

Conversions are the main way early retirees deliberately add MAGI. They're the volume knob you turn up when you have room. Most people do them late in the year, when the rest of the year's income is known.

4. HSA contributions

For 2026 the HSA limit is $4,400 self-only or $8,750 family, plus a $1,000 catch-up at 55 or older. Contributions are an above-the-line deduction, so they reduce MAGI dollar for dollar. Starting in 2026, bronze and catastrophic plans are treated as HSA-compatible. See HSA-eligible plans for early retirees.

5. Retirement contributions from side income

If you have self-employment income, a SEP-IRA or solo 401(k) deferral can reduce AGI. Pre-tax contributions to a traditional IRA may also help if you're eligible to deduct them.

6. Asset location

Holding bond funds and REITs inside IRAs keeps their payouts out of current MAGI. Broad index funds in taxable accounts tend to throw off modest, mostly qualified dividends, but those dividends still count.

Estimating income for the year ahead

The marketplace bases advance credits on expected income for the coverage year, not last year's. That is an advantage for retirees, whose last year often included a salary.

1. Start with last year's AGI as a sanity check, then remove income that won't recur, like wages.
2. Project dividends and interest from current balances and yields.
3. Decide your planned gains and Roth conversion amount.
4. Add tax-exempt interest and all Social Security benefits.
5. Subtract expected HSA and retirement contributions.
6. Leave a buffer for fund distributions and surprises.

Keep a short worksheet with your assumptions. If the estimate is off, you'll reconcile it on Form 8962 and, starting with 2026, there is no cap on repaying excess advance credits. Update the marketplace when anything material changes. See premium tax credit reconciliation.

Example: a couple setting their dial

Illustration: Frugal Fran, 58, and her spouse, 60, retired last spring. Household of two, so for 2026 coverage 100% FPL is $21,150 and the cliff sits at $84,600. Assumptions for the year:

At $22,250 they are just above 100% FPL. They now have about $62,350 of room before the cliff. Suppose they want a buffer of $5,000 and a top-of-12%-bracket conversion. They choose a $50,000 Roth conversion in December, landing MAGI at $72,250, or about 341.6% of FPL. At 9.96%, their expected contribution is roughly $7,196 for the year. If their benchmark plan costs $17,000, the credit is about $9,804.

Now compare a careless version: the same couple holds an extra $250,000 in munis and forgets about a $14,000 year-end fund distribution. MAGI lands at about $93,750, past the cliff. Credit: zero. The conversion was a good idea; the missing worksheet was not.

A multi-year MAGI plan for the bridge to Medicare

MAGI management works best as a multi-year plan, not an annual scramble. Picture the years between your last paycheck and Medicare as a row of buckets. Each bucket has a ceiling (the 400% line, or a lower target if you want a bigger credit) and a floor (100% of FPL, below which you may land in Medicaid or the coverage gap). Your job is to pour income into each bucket so it lands between floor and ceiling.

• Year of retirement: often already full because of wages. Many households skip conversions this year.
• Middle years: the sweet spot. Low earned income, room for conversions and gains, subsidies available.
• Year one spouse turns 65: that spouse moves to Medicare, household size for marketplace purposes may stay the same for tax, but only the younger spouse needs a marketplace plan, so the benchmark premium drops. The math changes.
• After both are on Medicare: the ACA cliff no longer matters, but IRMAA uses income from two years earlier, so conversions at 63 and 64 echo into Medicare premiums at 65 and 66. See Medicare Part B premiums and IRMAA.

Write the plan down once, then adjust every fall. It takes an hour and it is one of the highest-paying hours of early retirement.

When to deliberately accept higher MAGI

Lower MAGI isn't always better. A household with a huge pre-tax balance may face larger required minimum distributions later, pushing them into higher brackets for decades. Paying some tax now through conversions can cost a slice of subsidy today and save more later. Likewise, a one-time sale of a concentrated stock position or a rental property may be worth doing in a single year and simply skipping the credit that year.

The test is lifetime cost: subsidy lost plus tax paid now versus tax avoided later. That comparison is personal and assumption-heavy, which is why it deserves a spreadsheet rather than a vibe.

Common mistakes

• Using the IRMAA or Roth-contribution definition of MAGI instead of the marketplace definition.
• Forgetting a dependent's income when the dependent must file.
• Counting the full sale price of shares instead of the gain.
• Assuming an HSA contribution works without an HSA-compatible plan.
• Waiting until April to discover that December's distribution blew the estimate.

For the cliff mechanics see the ACA subsidy cliff guide, and for very low incomes see the Medicaid gap, which is the other edge of the same dial.