Who Runs Medicare and How It's Organized

Medicare is run by the Centers for Medicare & Medicaid Services, a federal agency under the U.S. Department of Health and Human Services

The Centers for Medicare & Medicaid Services (CMS) is the government office that manages Medicare. CMS sets the rules for what Medicare covers, how much it pays doctors and hospitals, and who can enroll. It is part of the Department of Health and Human Services, which is a cabinet-level agency of the federal government.

CMS does not deliver care itself — it pays for it. Doctors, hospitals, and other providers bill CMS when they treat a Medicare patient. CMS also contracts with private insurance companies to handle some of the day-to-day work of processing claims and paying providers.

Key Takeaways

The Centers for Medicare & Medicaid Services (CMS), a federal agency, sets Medicare policy and oversees the entire program.
Private insurance companies called Medicare Advantage plans and Medigap insurers handle claims and customer service under CMS rules.
The Social Security Administration handles Medicare enrollment and determines who is may be able to access based on age and work history.
Your state Medicaid office runs Medicaid separately, even though CMS oversees both programs.
You contact CMS directly through Medicare.gov or 1-800-MEDICARE for questions about coverage rules and program policy.

How CMS divides Medicare work among different organizations

CMS itself is headquartered in Baltimore, Maryland, and has regional offices across the country. However, CMS contracts with private companies to do much of the actual work. Medicare Advantage plans (also called Part C plans) are private insurance companies that CMS pays to cover all of your Medicare benefits. Medigap insurers are private companies that sell supplemental coverage to people on Original Medicare. These private companies process your claims, pay your providers, and answer your customer service calls — but they must follow CMS rules.

CMS also contracts with companies called Medicare Administrative Contractors (MACs) to handle claims processing and provider payments in different regions of the country. If you are on Original Medicare (Parts A and B), your claim goes to the MAC in your region, not directly to CMS.

The Social Security Administration's role in enrollment

The Social Security Administration (SSA) handles Medicare enrollment and determines whether you meet the age and work history requirements. When you turn 65, you contact Social Security to enroll in Medicare, not CMS directly. Social Security also maintains your earnings record, which determines whether you pay a premium for Part A (hospital insurance) and how much your Part B premium is.

Social Security and CMS share information about who is enrolled and when coverage begins. If you miss your enrollment important date, Social Security can tell you whether you owe a late penalty and how much it will be.

State Medicaid offices and the relationship to Medicare

Medicaid is a separate program from Medicare, even though CMS oversees both. Your state Medicaid office runs Medicaid in your state and decides who is may be able to access based on income and other factors. Some people are covered by both Medicare and Medicaid — they are called dual may be able to access — but the two programs are managed separately.

If you have questions about whether you may have access to for Medicaid or what it covers, contact your state Medicaid office, not CMS. Your state office can also tell you about programs that help pay Medicare premiums and out-of-pocket costs if you have low income.

How to contact CMS and Medicare directly

You can reach Medicare through Medicare.gov, the official website run by CMS. You can also call 1-800-MEDICARE (1-800-633-4227), which is the customer service line for Medicare. Both are available 24 hours a day, seven days a week. When you call, you reach staff who work for CMS contractors, but they follow CMS policy and can answer questions about coverage, enrollment, and your benefits.

If you have a complaint about your Medicare coverage or a provider, you can file it with CMS through Medicare.gov or by calling the number above. CMS takes complaints seriously and investigates them.

Regional Medicare offices and local resources

CMS has 10 regional offices across the country, each covering several states. These offices oversee Medicare in their region and work with state agencies, providers, and the public. You do not usually contact a regional office directly — you go through Medicare.gov or 1-800-MEDICARE — but the regional office is responsible for making sure Medicare works fairly in your area.

Some areas also have State Health Insurance information Programs (SHIPs), which are funded by CMS but run by your state. SHIP counselors are free and can answer questions about Medicare, help you understand your coverage, and help you file complaints. You can find your local SHIP through Medicare.gov or by calling 1-800-MEDICARE.

How CMS makes decisions about what Medicare covers

CMS has a process for deciding whether to cover a new drug, treatment, or service under Medicare. The Medicare Coverage with Evidence Development (CED) process allows CMS to cover a treatment while collecting more data about whether it works. CMS also publishes a National Coverage information (NCD) when it decides to cover or not cover something across the entire country, and Local Coverage Determinations (LCDs) when regional MACs make decisions for their area.

These decisions affect what your doctor can bill Medicare for and what you may have to pay out of pocket. If your doctor says Medicare will not cover something, you can ask whether CMS has made a national or local coverage decision about it, and your doctor can help you understand why.

Frequently Asked Questions

Can I appeal a decision CMS made about my coverage?

Yes. If CMS or your Medicare plan denies a claim or says something is not covered, you have the right to appeal. The appeal process has several levels, starting with a reconsideration by the same organization that made the first decision. You can find the appeal process on your Explanation of Benefits or by calling 1-800-MEDICARE.

Does CMS run Medicare Advantage plans?

No. CMS pays private insurance companies to run Medicare Advantage plans, but the insurance companies make day-to-day decisions about coverage and claims. However, these companies must follow CMS rules and offer at least the same benefits as Original Medicare. If you have a complaint about your Medicare Advantage plan, you can file it with CMS.

Who decides how much doctors get paid under Medicare?

CMS sets the payment rates that Medicare pays doctors and hospitals. These rates are based on a formula that CMS updates each year. Doctors must accept the Medicare rate as payment in full — they cannot charge you more than what Medicare allows, with rare exceptions.

What if I disagree with a coverage decision CMS made?

You can submit a comment during the public comment period when CMS is considering a new coverage decision. CMS publishes proposed decisions and accepts feedback before making a final decision. You can also contact your elected representatives in Congress, who can ask CMS to reconsider a decision.

Is Medicare.gov run by CMS?

Yes. Medicare.gov is the official website of CMS and Medicare. It is where you can enroll in Medicare, view your coverage, find providers, and get information about your benefits. The site is maintained by CMS contractors, but CMS is responsible for the content and accuracy.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.