Medicare is the primary payer when someone has both Medicare and Medicaid. This means Medicare processes and pays its share of a claim first, and Medicaid picks up some or all of the remaining costs second. This rule applies universally to every service that Medicare covers, regardless of which state you live in. About 12.8 million people in the United States are enrolled in both programs simultaneously, a group often called “dual eligibles.”
What “Primary” and “Secondary” Mean for Your Bills
When you have two forms of health coverage, one program always pays first. That’s the primary payer. The secondary payer then reviews what’s left and covers its portion. For dual eligibles, the sequence works like this: your provider submits a claim to Medicare, Medicare pays what it owes, and whatever balance remains (deductibles, copays, coinsurance) gets sent to Medicaid for potential payment.
In most cases, you don’t need to do anything to make this happen. Through a federal system called the Coordination of Benefits Agreement (COBA), Medicare automatically forwards processed claims to Medicaid. The Benefits Coordination and Recovery Center administers this crossover process nationally, so claims move from Medicare to your state’s Medicaid agency without you or your doctor manually submitting a second bill. Medicaid managed care organizations also participate in this automated crossover system.
What Medicaid Covers After Medicare Pays
Medicaid’s role as secondary payer depends on what type of dual eligibility you have. There are two broad categories: full-benefit and partial-benefit.
Full-benefit dual eligibles receive complete Medicaid coverage on top of Medicare. For these individuals, Medicaid typically covers the cost-sharing that Medicare leaves behind, including deductibles and copayments. It also covers services that Medicare doesn’t offer at all, such as long-term nursing home care, dental, vision, and transportation to medical appointments. The specifics vary by state, since each state runs its own Medicaid program with its own benefit package.
Partial-benefit dual eligibles get more limited help. The most common partial-benefit category is the Qualified Medicare Beneficiary (QMB) program. If you’re enrolled in QMB, Medicaid pays your Medicare Part A and Part B premiums, and you have no legal obligation to pay any Medicare deductibles, coinsurance, or copayments for covered services. Other partial-benefit categories may cover only your premiums without the cost-sharing protection.
Long-Term Care: Where Medicaid Becomes the Main Payer
One major area where the primary/secondary dynamic shifts is long-term nursing home care. Medicare generally does not cover custodial care in a nursing facility. It covers short-term stays for rehabilitation after a hospital admission, but once you need ongoing help with daily activities like bathing, dressing, and eating, Medicare stops paying.
Most people who enter nursing homes start by paying out of pocket. Once their resources are spent down enough to qualify for Medicaid, Medicaid becomes the primary payer for the nursing home itself. However, Medicare still covers what it normally covers: hospital care, doctor visits, prescription drugs, and medical supplies you need while living in the facility. So even in a nursing home where Medicaid pays for your room and board, Medicare remains primary for medical services.
How States Handle the Details Differently
While the “Medicare pays first” rule is federal law and doesn’t change by state, the way states manage dual-eligible claims behind the scenes does vary. Some states exclude dual eligibles from Medicaid managed care entirely, handling all secondary payment responsibilities directly. Others enroll dual eligibles in Medicaid managed care organizations and delegate the responsibility for coordinating with Medicare to those plans, adjusting their payments accordingly. A few states take a hybrid approach, keeping some coordination responsibilities while handing others off to managed care.
For you as a patient, the practical impact is mostly invisible. What matters is whether your providers accept both Medicare and Medicaid, and whether they’re set up to process crossover claims. If you’re enrolled in a dual eligible special needs plan (D-SNP), a type of Medicare Advantage plan designed specifically for people with both programs, much of this coordination is built in. Starting in 2027, D-SNPs will be required to issue a single integrated ID card that works for both Medicare and Medicaid, replacing the current system where you may carry two separate cards.
Prescription Drug Coverage for Dual Eligibles
Medicare Part D is primary for prescription drugs. Dual eligibles automatically qualify for Extra Help (also called the Low-Income Subsidy), which dramatically reduces premiums, deductibles, and copayments for medications. For covered insulin products, the out-of-pocket cost is capped at $35 per month or 25% of the negotiated price, whichever is less.
If you’re a full-benefit dual eligible, your Part D copays are minimal, often just a few dollars per prescription. Medicaid may also cover certain drugs that Part D excludes, such as over-the-counter medications or specific drug classes that vary by state. In these cases, Medicaid isn’t acting as a secondary payer so much as filling in gaps that Medicare’s drug benefit doesn’t address at all.
What to Do If a Provider Bills You Directly
If you’re enrolled in both Medicare and Medicaid, you should rarely owe anything out of pocket for Medicare-covered services. QMB enrollees in particular are legally protected from balance billing. If a provider sends you a bill for Medicare cost-sharing, that provider is not allowed to collect it from you. They must bill Medicaid instead.
Problems sometimes arise when a provider doesn’t realize you have Medicaid as secondary coverage, or when the automatic crossover system doesn’t transmit a claim correctly. If you receive a bill you believe should have been covered, contact your state Medicaid agency or the provider’s billing office and confirm they have your Medicaid information on file. Keeping both your Medicare and Medicaid cards available at every appointment helps prevent these billing errors from happening in the first place.