How to Manage Your MAGI to Stay Under the Subsidy Cliff

Let me say the important thing first: I am a licensed insurance broker, not a CPA or a tax attorney. Nothing here is tax advice, and you should not act on any of it without your tax preparer. What I can do is explain which number the marketplace looks at, because that is an insurance question, and because I watch people lose subsidies over it every year.

The number is Modified Adjusted Gross Income. Every dollar of your premium tax credit is calculated from it.

What MAGI actually is

Start with the Adjusted Gross Income on your tax return. Then add back three things:

• Tax-exempt interest
• The portion of your Social Security benefits that is not taxable
• Excluded foreign earned income

That is the entire formula. Three add-backs, nothing else.

If your household includes dependents who are required to file their own returns, their modified AGI is added too.

The two that surprise people

Two of those add-backs cause more damage than everything else combined, because they are invisible on a normal tax return.

Municipal bond interest

You may hold municipal bonds precisely because the interest is federally tax-free. For income tax purposes, it is. For marketplace subsidy purposes, it is added straight back in.

This is the single most common way I see people cross the line without knowing they were near it. The interest never appears in your taxable income, so it never enters your mental arithmetic, and it counts here in full.

The non-taxable portion of Social Security

If you are drawing Social Security before 65 — a survivor benefit, or a claim you started early — you report the gross benefit to the marketplace, not the taxable portion from your 1040.

Say you draw $40,000 a year in benefits and only part of it is taxable on your 1040. The marketplace wants the full $40,000. That gap alone can move a household a full bracket.

What counts, plainly

Counts toward MAGI: wages, self-employment income, capital gains, interest and dividends including qualified dividends, rental income, withdrawals from traditional IRAs and 401(k)s, Roth conversions, pension and annuity income, unemployment compensation, and alimony from divorces finalized before 2019.

Does not count: qualified distributions from a Roth account you already funded, child support, gifts and inheritances, Supplemental Security Income, VA disability payments, loan proceeds, and alimony from divorces finalized in 2019 or later.

The levers you actually have

Roth conversion timing

A Roth conversion is fully taxable in the year you do it, and it raises your MAGI dollar for dollar. Between roughly 60 and 65, conversions and marketplace coverage pull against each other directly.

The window where conversions are cheapest — after your paychecks stop, before Required Minimum Distributions start — is exactly the window where you depend on a subsidy. There is no clean answer. There is only arithmetic: compare the tax saved over your lifetime against the subsidy given up this year, including the possibility of repaying an entire year's advance credit with no cap if the conversion pushes you over 400%.

Some people convert aggressively at 65 once they are on Medicare and the subsidy is no longer at risk. Some convert in small annual slices that keep them under the line. Your tax preparer should run both.

HSA contributions

If you are enrolled in an HSA-qualified high-deductible plan, your contribution is an above-the-line deduction. It lowers AGI, so it lowers MAGI.

This is one of the few clean levers you have, and it has a useful property: you can generally make the contribution up until the tax filing deadline. That means you can look at your actual finished income in March and still move the number.

Not sure where your projected income lands? Run it through the subsidy estimator before you make any year-end moves.

Capital gains and loss harvesting

Realized gains count. Realized losses offset those gains, and net losses beyond that are limited to $3,000 per year against ordinary income, with the remainder carried forward.

The practical point for someone near the cliff: you often control the timing of a sale. Splitting a large position across two tax years, or pairing a gain with a loss you were going to harvest anyway, can be the difference between keeping and losing a year of subsidy.

Deductible retirement contributions

If you still have earned income — consulting, part-time work, a small business — deductible contributions to a traditional IRA or a solo 401(k) reduce AGI. For someone semi-retired, this is frequently overlooked.

What to do

Project your income for the full year now, not in December. Include the things that are easy to miss: fund distributions you do not control, interest on cash you moved into treasuries, the gross Social Security figure rather than the taxable one.

Then take that projection to your tax preparer and ask one question: what is my expected MAGI, and how close is it to 400% of the Federal Poverty Level for my household size?

If the answer is anywhere near, coordinate every income decision for the rest of the year with them. And keep me in the loop on the coverage side, because if you do end up over the line, the plan you should be buying is a different plan.

Report income changes to the marketplace as they happen rather than waiting. Adjusting your advance credit mid-year is uncomfortable. Repaying twelve months of it at once is worse.