ACA Subsidy Calculator

How ACA subsidies work

The Affordable Care Act provides Premium Tax Credits (subsidies) to reduce the cost of marketplace health insurance. The subsidy is based on how your household Modified Adjusted Gross Income (MAGI) compares to the Federal Poverty Level (FPL) for your household size and state.

If your MAGI is between 100% and 400% of FPL, you qualify for a subsidy that caps your premium at a percentage of your income. The cap ranges from about 2% of income at the low end (near 100% of FPL) to roughly 10% at the high end (near 400% of FPL). Above 400% of FPL, there is no subsidy at all. The government pays the difference between the full premium and your capped amount directly to the insurance company.

For early retirees, this is one of the largest financial levers in retirement. A couple retiring at 55 with $60,000 in MAGI might receive $20,000 to $30,000 per year in subsidies. But if they do a $50,000 Roth conversion and push their MAGI to $110,000, they could lose most or all of that subsidy. The math is not obvious, and getting it wrong can cost tens of thousands.

The ACA subsidy cliff and phase-out

There is a hard cliff at 400% of FPL. Earn one dollar over and you lose the entire subsidy, potentially adding $15,000 or more to your annual healthcare cost. A temporary enhancement under the Inflation Reduction Act removed this cliff and capped premiums at 8.5% of income for everyone, but that enhancement expired at the end of 2025 and Congress did not renew it. The original rules, cliff included, are back in effect.

Below the cliff, the phase-out is already steep. As your income rises, the subsidy shrinks because you are paying a larger share of a premium that also increases with age. A 60-year-old whose MAGI goes from $50,000 to $80,000 might see their subsidy drop by several thousand dollars a year even while staying under 400% of FPL. The cost of earning more is not just the income tax. It is the lost subsidy as well.

Why early retirees need to manage MAGI carefully

For early retirees (typically ages 50 to 64), ACA insurance is often the only realistic option for health coverage before Medicare. Employer coverage is gone. COBRA runs out after 18 months. Individual underwritten policies are expensive and limited. The ACA marketplace, with subsidies, is the path.

The challenge is that retirement creates multiple competing goals for your MAGI:

1. Keep MAGI low enough to maximize ACA subsidies. Every dollar of MAGI above the optimal level reduces your subsidy and increases your healthcare cost.
2. Convert enough to Roth to reduce future RMDs. Roth conversions increase MAGI, creating a direct conflict with the ACA goal.
3. Generate enough spendable income to live on. You need to withdraw from accounts to pay expenses, and those withdrawals also affect MAGI.
4. Stay within tax brackets. Even within the ACA subsidy zone, higher MAGI means higher income tax rates.

These goals conflict with each other. There is no single right answer. The optimal MAGI target changes every year based on your age, account balances, spending needs, and the specific ACA premium rates in your area. Year-by-year modeling is the only way to see the full picture.

How ThunderHarbor models ACA costs year by year

ThunderHarbor calculates your ACA premium, subsidy, and net cost for every year between your retirement and age 65, when you transition to Medicare. For each year:

1. Calculates your full MAGI including all income sources: salary, pension, Social Security, withdrawals, Roth conversions, capital gains, and dividends
2. Applies the age-rating factor. ACA premiums increase with age, typically 3x higher at age 64 vs. age 21, which ThunderHarbor models each year as you age
3. Applies your state's benchmark premium: the second-lowest-cost Silver plan in your rating area, which varies significantly by state and county
4. Calculates the Premium Tax Credit based on your MAGI relative to FPL, using the current applicable-percentage table and the 400% FPL hard cliff
5. Shows your net premium cost after subsidy, and the effective marginal cost of additional income in terms of lost subsidies

When the Roth conversion optimizer is enabled, ThunderHarbor caps conversions to preserve ACA subsidies in years where the subsidy loss would outweigh the future tax benefit. You can see exactly how much conversion room you have before it starts costing more in subsidies than it saves in future taxes.

The age factor: why ACA costs change every year

ACA premiums are age-rated, meaning the full premium increases as you get older. A plan that costs $400/month at age 50 might cost $700/month at age 60 and $900/month at age 63. The subsidy calculation uses this age-rated premium as the benchmark, so your subsidy also increases with age, but not always enough to offset the premium increase.

This creates a counterintuitive dynamic: your net out-of-pocket ACA cost can rise sharply in your late 50s and early 60s even if your income stays the same, because the age-rated premium grows faster than the subsidy. ThunderHarbor models this year by year so you can plan for the rising cost curve rather than being surprised by it.

State variations add another layer. Some states have additional subsidies (like California's Covered California program or New York's Essential Plan). Some states have higher base premiums than others. ThunderHarbor applies state-specific adjustments so the projection reflects the actual costs you will face, not a national average.

Frequently asked questions