How to find the right payer for Medicare claims

Medicare is complex. To file a claim, you need to know which part of Medicare you’re dealing with and which payer handles it.

This guide explains how Medicare claims work and walks you through the steps to find the right payer.

The parts of Medicare

Medicare has four parts, each covering different services. The government runs two, and private companies run two.

Government-run

• Part A – Covers hospital benefits, like inpatient stays, skilled nursing facilities, and hospice care.
  
  

• Part B – Covers medical benefits like doctor visits and preventive care.

Both Part A and Part B are run by the Centers for Medicare & Medicaid Services (CMS), a U.S. federal government agency. Together, Parts A and B are called “Original Medicare” or “Traditional Medicare.”

Privately-run Medicare plans

• Part C (Medicare Advantage) – Private health plans that replace Medicare Part A and Part B benefits. Many of these plans include extra benefits beyond what Part A and Part B offer, like drug, dental, or vision coverage.
  
  Patients can be covered by either Original Medicare (Part A and Part B) or a Part C (Medicare Advantage) plan, but not both.
  
  

• Part D – Prescription drug benefits, offered through private plans. Part D coverage is optional. It can be combined with Original Medicare or Part C.

Medigap
Medigap, or Medicare Supplement Insurance, isn’t part of Medicare. It’s a private plan that helps cover costs that Part A and Part B don’t.

Medigap plans are run by private payers and are designed to complement Medicare coverage. Secondary claims for Medigap are covered later in this guide.

Which type of Medicare does the patient have?
Patients covered by Medicare Part A and Part B will have a government-issued Medicare card. For example:

Patients on a Part C (Medicare Advantage) plan will have an insurance card from the private payer. Some payers have separate payer IDs for Medicare Advantage plans and other lines of business, like employer-sponsored plans. For example: CareFirst Medicare Advantage and Blue Cross Illinois Medicare Advantage.

Similarly, patients on Part D have a separate prescription drug card from their plan.

If you’re submitting a claim for Medicare Part C or Part D, send it directly to the plan’s private payer, just like any other claim. For guidance, see our claims processing docs.

Important: The rest of this guide focuses on Medicare Part A and Part B claims.

MACs

CMS doesn’t process Medicare Part A or Part B claims itself. Instead, it uses regional payers called Medicare Administrative Contractors (MACs).

Each MAC processes Part A and Part B claims for services done in that region. Stedi connects to all MACs.

Types of MACs
There are three different types of MACs:

• A/B MACs – Handle Part A and Part B claims.
  
  

• Home health and hospice (HH+H) MACs – A subset of A/B MACs that handle home health and hospice claims.
  
  

• Durable medical equipment (DME) MACs – MACs that handle claims for medical equipment that patients keep and use at home. Think wheelchairs, oxygen tanks, and CPAP machines.

Jurisdictions
Each MAC covers specific states or territories, called a jurisdiction. You send Medicare Part A and Part B claims to the MAC for the jurisdiction where the service was provided.

For current lists and maps of MACs and their jurisdictions, see Who are the MACs on the CMS site. For example, as of October 2025, the MACs and jurisdictions for California are as follows:

MAC assignments can change each federal fiscal year when contracts are renewed. Check the current MACs on the CMS site before submitting a claim.

Medicare (CMS) eligibility checks

Many providers run an eligibility check to verify the patient’s Medicare coverage before submitting a claim. This helps avoid errors and denied claims.

Send Medicare Part A and Part B eligibility checks to CMS (payer ID: CMS), not to a MAC. Unlike most payers, CMS requires transaction enrollment before a provider can start sending them eligibility checks.

Important: Don’t send eligibility checks for Medicare Part C (Medicare Advantage) or Part D to CMS. Send those checks to the plan’s private payer instead.

How to find the payer for Medicare claims

Follow these steps to find the correct payer and payer ID for your Medicare Part A and Part B claims:

1. Determine the claim type.
   To find the right MAC, you first need to know whether the claim is for Medicare Part A, Part B, home health and hospice (HH+H) care, or durable medical equipment (DME).
   You can usually tell based on the billing provider and what service was provided. For example:

   • A home health agency billing for skilled nursing visits would submit a claim for HH+H.

   • A hospital billing for an inpatient stay would submit a claim for Medicare Part A.

   • An outpatient clinic billing for a check-up would submit a claim for Part B.

   
   Based on the Medicare Claims Processing Manual, if an encounter included both procedures and DME, split the DME portion into a separate claim, even if it’ll be sent to the same MAC.
   
   

2. Find the right MAC.
   Use CMS’s MAC lists and maps to find the MAC for where the service happened. Use the provider’s location during care, not the patient’s home address, even for telehealth visits.
   
   The only exception is Medicare Railroad, which has one nationwide MAC (Palmetto GBA) that handles all Railroad Retirement Board claims.
   
   

3. Look up the payer ID.
   Use the Stedi Payer Network or the Stedi Payers API to search for the MAC and get its payer ID.
   
   Some MACs have specific payer IDs for different states, regions, or claim types. MAC payer names often contain “Medicare” along with the state name and “Part B.” For example: Medicare Georgia Part A or Medicare Part B Puerto Rico (First Coast).

   
   

4. Submit your claim using the payer ID.
   You typically use institutional claims for Medicare Part A or HH+H services. You typically use professional claims for Medicare Part B or DME services.
   
   Dental claims are only covered by Medicare when dental work is required for a covered medical procedure.
   
   In the claim, use the patient’s Medicare Beneficiary Identifier (MBI) as the member ID. An MBI is a unique ID for a Medicare beneficiary. It’s listed on the patient’s Medicare card.

   
   If you don’t have the patient’s MBI, you can get it using an MBI lookup with the patient’s SSN and demographic details.
   
   For additional guidance on submitting claims, see our docs:

   • Submitting professional claims

   • Submitting institutional claims

   • Submitting dental claims

Example
You want to submit a professional claim for a doctor visit with an established patient. The visit took place in Los Angeles, California, and is covered under Medicare Part B.

Based on CMS’s MAC lists and maps, the Medicare Part A/B MAC for California is Noridian. Use the Stedi Payer Network or Search Payers endpoint to search for noridian. Using the endpoint: 

curl --request GET \
  --url "https://healthcare.us.stedi.com/2024-04-01/payers/search?query=noridian" \
  --header "Authorization: <api-key>" | jq

One of the top results is Medicare Southern California Part B (payer ID 01182):

{
  "items": [
    ...
    {
      "payer": {
        "displayName": "Medicare Southern California Part B",
        "primaryPayerId": "01182",
        ...
      },
      ...
    },
    ...
  ],
}

Use the payer ID to submit the claim using the Professional Claims JSON endpoint:

curl --request POST \
  --url https://healthcare.us.stedi.com/2024-04-01/change/medicalnetwork/professionalclaims/v3/submission \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '{
  "tradingPartnerServiceId": "01182",  // Payer ID for Medicare Southern California Part B
  "claimInformation": {
    ...
    "serviceLines": [
      {
        "professionalService": {
          "procedureIdentifier": "HC",  // HCPCS/CPT procedure codes
          "procedureCode": "99213",     // CPT code for an established patient visit
          ...
        },
        ...
      }
    ]
  },
  "subscriber": {
    "memberId": "1EG4TE5MK73",  // The patient's MBI
    ...
  },
  ...
}'

Secondary claims for Medigap

Most Medigap payers participate in Medicare’s Coordination of Benefits Agreement (COBA) Program. In these cases, the MAC will automatically forward secondary claims to the Medigap payer for you. This is called a crossover claim.

Here's how Medigap crossover claims work:

• You send the primary claim to Medicare through the right MAC.

• The MAC processes the claim and pays Medicare’s share (if any).

• The MAC automatically forwards the claim to the patient’s Medigap payer.

• The Medigap processes the claim and pays its share (if any).

In these cases, you don’t need to submit a separate secondary claim.

You’ll know a Medicare claim was forwarded if the 835 ERA for the claim includes a claimStatusCode set to either 19, 20, or 21. For more details, see our crossover claims docs.

If the MAC doesn't forward the claim automatically, you'll need to submit the secondary claim to the Medigap payer yourself. For guidance, see our docs:

• Secondary professional claims

• Secondary institutional claims

• Secondary dental claims

Get started

Once you know the MAC’s payer ID, submitting a Medicare claim is straightforward.

Stedi’s Basic plan lets you submit Medicare claims to any MAC for free. You get 100 free claims each month. Signup takes less than two minutes and doesn’t require a credit card.