Medicare assignment is an agreement between your doctor and Medicare to accept the Medicare-approved amount as full payment for a covered service. When a provider accepts assignment, they bill Medicare directly, Medicare pays its 80% share, and you pay the remaining 20% coinsurance (after your annual deductible). That’s it. The provider cannot charge you anything beyond that approved amount.
Whether your doctor accepts assignment has a direct impact on what you pay out of pocket, and in some cases, whether Medicare covers any of the cost at all.
How Assignment Works in Practice
When a doctor accepts assignment, three things happen. First, they agree that Medicare’s approved amount is the total price for the service. Second, Medicare pays them 80% of that approved amount. Third, you owe the remaining 20% coinsurance, plus any portion of your Part B deductible you haven’t met yet. The provider handles the claim submission to Medicare, so you don’t need to file paperwork yourself.
For example, if Medicare’s approved amount for an office visit is $200, Medicare pays the doctor $160 and you pay $40. The doctor can’t add extra charges on top of that $200. This predictability is one of the biggest advantages of seeing a provider who accepts assignment.
Participating vs. Non-Participating Providers
Doctors choose one of three relationships with Medicare, and each one changes what you’ll pay.
Participating providers have signed an agreement to accept assignment on every Medicare claim for the entire calendar year. They always accept the Medicare-approved amount as payment in full. About 98% of providers fall into this category, according to the Centers for Medicare & Medicaid Services’ participation data for 2024.
Non-participating providers haven’t signed that annual agreement but still enroll in Medicare. They can decide on a claim-by-claim basis whether to accept assignment. When they don’t accept assignment, they can charge you more than the Medicare-approved amount. However, federal law caps this extra charge. Non-participating providers cannot bill more than 115% of the Medicare fee schedule amount for their services. This cap is called the “limiting charge.”
So if Medicare’s approved amount for a service is $200, a non-participating provider who doesn’t accept assignment could charge up to $230. You’d be responsible for the full difference between what Medicare pays and what the provider charges, up to that 115% ceiling. You may also need to pay the provider upfront and submit the claim to Medicare yourself for reimbursement.
Opted-out providers have formally withdrawn from Medicare entirely. They sign a two-year opt-out affidavit and cannot bill Medicare at all during that period. If you see an opted-out provider, you must sign a private contract agreeing that neither of you will submit claims to Medicare for those services. Medicare will not reimburse any portion of the cost. There is no cap on what these providers can charge. This arrangement is permitted for physicians, nurse practitioners, clinical psychologists, podiatrists, dentists, optometrists, and several other provider types.
What the Limiting Charge Means for Your Bill
The limiting charge is the single most important number to understand when you see a non-participating provider who doesn’t accept assignment. It sets the legal maximum they can charge at 115% of the fee schedule amount for non-participating suppliers. In practice, this means you could pay up to 15% more than Medicare’s approved rate for the same service you’d get from a participating doctor.
That 15% difference applies on top of your regular 20% coinsurance. The math adds up quickly for expensive services like imaging, procedures, or specialist consultations. Over the course of a year with multiple medical visits, choosing providers who accept assignment can save you hundreds of dollars.
Some states have additional protections that limit or prohibit balance billing beyond the federal rules. If you live in Connecticut, Massachusetts, Minnesota, New York, Ohio, Pennsylvania, Rhode Island, or Vermont, your state may restrict what non-participating providers can charge Medicare patients.
Assignment Under Medicare Advantage
Medicare Advantage (Part C) plans work differently from Original Medicare, and the assignment rules shift accordingly. If your plan is an HMO or PPO, the plan contracts directly with a network of providers. Staying in-network means the plan’s negotiated rates apply, and your costs follow the plan’s copay or coinsurance structure rather than the 80/20 split of Original Medicare.
When you see an out-of-network provider under a Medicare Advantage plan, that provider must generally be reimbursed at least the Original Medicare rate. Physicians who are non-participating with Medicare and don’t accept assignment can still balance bill up to the same 115% limiting charge. However, if a provider does balance bill a Medicare Advantage enrollee, the plan is legally required to cover the extra amount and protect you from charges above your plan’s stated cost-sharing.
Private fee-for-service (PFFS) plans are an exception. These plans can set their own fee schedules and may allow providers to balance bill up to 15% above the Medicare amount, potentially exceeding what Original Medicare would permit. If you’re in a PFFS plan, it’s worth reviewing the plan’s terms carefully before seeing a non-network provider.
Certain Services Always Require Assignment
Some Medicare services require the provider to accept assignment regardless of their participation status. Clinical lab services covered under Part B must always be billed on assignment. So must durable medical equipment for patients who qualify for both Medicare and Medicaid. If you’re enrolled in a Medicare Savings Program that helps pay your premiums or cost-sharing, providers are also required to accept assignment for your care. In these situations, the provider cannot charge you more than the Medicare-approved amount, even if they’re non-participating.
How to Check a Provider’s Assignment Status
Before scheduling an appointment, you can verify whether a provider accepts Medicare assignment using the Care Compare tool on Medicare.gov. The tool lets you search for physicians, hospitals, nursing homes, and other Medicare-approved providers by location and specialty. Each provider listing indicates whether they participate in Medicare.
You can also call the provider’s office directly and ask two specific questions: “Do you accept Medicare?” and “Do you accept Medicare assignment?” These are not the same thing. A doctor can accept Medicare patients without accepting assignment, meaning they may bill you above the approved amount. Getting a clear answer to both questions before your visit prevents surprise charges.
If you have Original Medicare and want the most predictable costs, choosing participating providers is the simplest approach. With 98% of providers participating, most people won’t have trouble finding one. But if you need to see a specialist or provider who doesn’t accept assignment, knowing the limiting charge rules helps you estimate your actual out-of-pocket cost before you commit.