If you bought your health insurance through Covered California or the ACA Marketplace because you didn't have employer coverage, turning 65 changes your situation in an important way, and not always an obvious one. This guide explains exactly what happens to your ACA plan and subsidy as you approach Medicare, so you make the transition at the right time and don't lose money over a missed deadline.
Why Medicare, in practice, replaces your ACA plan
ACA premium subsidies (premium tax credits) are designed for people who don't have access to other affordable 'minimum essential coverage,' and premium-free Medicare Part A counts as that minimum essential coverage. As soon as you qualify for premium-free Medicare Part A — generally at age 65 if you or your spouse have enough work credits — you lose eligibility for the ACA subsidy going forward, regardless of whether you activate Part B at that point.
In other words, it's not that Medicare legally 'forces' you to cancel your ACA plan, but keeping it without the subsidy is almost always far more expensive than switching to Medicare, and delaying Medicare without a valid reason can also result in a lifelong penalty.
Availability, cost, benefits, and eligibility vary by person, product, contract, and insurance company, as well as by your service area. Guarantees are subject to the claims-paying ability of the issuing insurance company. Karla Arámburo is not affiliated with or endorsed by Medicare or the federal government.
What exactly happens to your ACA subsidy
The subsidy is calculated month by month based on your eligibility. From the month your premium-free Medicare Part A takes effect, you no longer qualify for the subsidy, even if you keep paying your ACA plan's full premium. If the Marketplace doesn't learn of your Medicare eligibility and you keep receiving the subsidy, the difference gets reconciled when you file the following year's tax return, and you may have to repay that money to the IRS. That's why it's important to report your Medicare enrollment to Covered California as soon as it happens, not wait for tax season.
Enrollment timing: when to switch without a penalty or a gap
Your Initial Enrollment Period (IEP) for Medicare lasts seven months: it starts three months before your 65th birthday month, includes your birthday month, and ends three months after. Enrolling in Medicare Part A and Part B during the three months before your birthday generally lets your coverage start on the first day of your birthday month, with no gap between your ACA plan and Medicare. For more detail on this period, see our Initial Enrollment Period guide.
If you delay enrolling in Part B without valid active employment coverage, you can face a permanent penalty of 10% of the standard premium for each full 12-month period you delayed, on top of having to wait for a general enrollment period with coverage that doesn't start for months. See our late enrollment penalty guide to see exactly how it's calculated.
Cost differences: subsidized premium vs. Medicare's structure
| Aspect | ACA/Covered California plan | Medicare |
|---|---|---|
| Monthly premium | Can be very low or zero with a subsidy based on your income. | Standard Part B premium, plus the cost of Medicare Advantage or Medigap and Part D. |
| Network structure | Often a local HMO with a county-limited network. | Original Medicare is accepted by any provider who takes Medicare nationwide; Medicare Advantage uses its own network. |
| Annual adjustment | The subsidy and premium change based on reported income each year. | The Part B premium can rise with income (IRMAA) in high-income years. |
There's no single answer for which ends up cheaper; it depends on your income, your current subsidy, and the plans available in your area. We review the real numbers of your case before you make a decision.
Still working at 65 with an ACA plan?
It's important to distinguish between having active employer coverage from an employer with 20 or more employees (which can let you delay Medicare without a penalty) and having an ACA/Covered California plan because your employer doesn't offer insurance, or because you're self-employed. An ACA plan does not count as active employment-based coverage for Medicare purposes, so if your only coverage is an ACA plan, you generally need to enroll during your Initial Enrollment Period even if you're still working. For the case of coverage from a large employer, see our turning 65 and still working guide.
Practical steps to make the transition
First, mark the start of your Initial Enrollment Period on your calendar, three months before your 65th birthday. Second, enroll in Medicare Part A and Part B through Social Security before your birthday to avoid a coverage gap. Third, decide between Medicare Advantage or Original Medicare with Medigap and Part D — our Medicare Advantage guide helps you compare. Fourth, check your medication formulary against Part D with our Part D guide. And fifth, formally cancel your Covered California plan with the effective date of your Medicare coverage, not before, to avoid a period with no coverage.
Also review this year's specific dates in our 2026 Medicare enrollment dates guide.
Free bilingual help making this transition without mistakes
I am Karla Arámburo, an independent, bilingual insurance agent licensed in California. I review your current Covered California premium and subsidy against the Medicare Advantage or Medigap options available in your ZIP code with you, we calculate the exact dates for your Initial Enrollment Period, and coordinate canceling your ACA plan at the right time, in Spanish or English, at no cost to you. I also offer life insurance that accepts an ITIN for family members who don't have a Social Security number.
You can call or text (619) 321-8733 or schedule a free consultation. This page is general education, not individualized advice or a product recommendation.
Frequently asked questions
Do I automatically lose my Covered California plan when I turn 65?
Not automatically, but you should cancel it yourself once your Medicare coverage takes effect. If you don't cancel it, you can end up paying two premiums at once, and if you keep receiving an ACA subsidy after becoming Medicare-eligible without reporting it, you may have to repay that subsidy when you file your taxes.
Can I keep my Covered California plan instead of enrolling in Medicare?
You can technically decline Medicare, but in the large majority of cases it doesn't pay off: you will lose the ACA premium subsidy as soon as you become eligible for premium-free Medicare (Part A), and if you enroll in Medicare later, you will likely face a lifelong Part B penalty for each full year you delayed.
What happens to my ACA plan's subsidy if I have Medicare Part A but not Part B?
Having premium-free Part A generally disqualifies you from receiving an ACA premium subsidy going forward, even if you never activated Part B. The law treats Medicare Part A as already being 'minimum essential coverage,' so the subsidy stops applying from the month your Part A takes effect.
I'm still working at 65 with an ACA plan because my employer doesn't offer insurance. What should I do?
An ACA/Covered California plan does not count as active employer-based coverage for the purpose of delaying Medicare without a penalty, unlike a group plan from an employer with 20 or more employees. If you're still working but your only insurance is an ACA plan, you generally need to enroll in Medicare during your Initial Enrollment Period to avoid penalties.
Are Medicare Advantage or Medigap costs higher than my subsidized ACA plan?
It depends on your specific situation. If you were receiving a large ACA subsidy, your monthly premium may have been very low or even zero. With Medicare, you generally pay the standard Part B premium plus the cost of a Medicare Advantage plan or Medigap and Part D. We compare both scenarios with real numbers before you decide.
When should I start making this switch from ACA to Medicare?
Ideally during your Initial Enrollment Period, which lasts seven months around your 65th birthday: it starts three months before your birthday month and ends three months after. Enrolling before your birthday avoids a coverage gap between your ACA plan and the start of Medicare.
Can you help me compare my current Covered California plan against Medicare options?
Yes. I review your current premium, doctor network, medications, and ACA subsidy against the Medicare Advantage or Medigap options available in your ZIP code with you, so the transition happens at the right time and without surprises, at no cost to you.