Which Government Agency Runs Medicare and What That Means for You

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

The Centers for Medicare & Medicaid Services (CMS) is the federal agency that administers Medicare. CMS is not an independent agency — it sits inside the Department of Health and Human Services (HHS), which is a cabinet-level department of the federal government. This matters because it means Medicare policy comes from HHS leadership, but day-to-day operations, payment rules, and coverage decisions flow through CMS.

CMS also runs Medicaid and the Children's Health Insurance Program (CHIP), so it handles health coverage for a large portion of the U.S. population. The agency has regional offices in each state and maintains a national helpline and website where you can find information about your coverage, appeals, and enrollment periods.

Understanding that CMS is the entity behind Medicare helps you know where to direct questions and complaints. If you have a coverage dispute or need to understand why a claim was denied, CMS or its contractors are the bodies that made that decision.

Key Takeaways

The Centers for Medicare & Medicaid Services (CMS), part of the Department of Health and Human Services, is the federal agency that runs Medicare.
CMS sets coverage rules, payment amounts, and enrollment important date, but private insurance companies called Medicare Advantage plans and Part D drug plans are contracted to deliver the actual coverage.
Each state has a CMS regional office, and you can contact CMS directly through Medicare.gov or by calling 1-800-MEDICARE for questions about your coverage or appeals.
CMS also administers Medicaid and CHIP, making it the largest health insurance administrator in the federal government.

How CMS structures Medicare through private insurers

CMS does not deliver Medicare coverage directly to every beneficiary. Instead, the agency sets the rules and payment rates, then contracts with private insurance companies to actually provide the coverage. This structure applies to Medicare Advantage (Part C) and prescription drug coverage (Part D). For Original Medicare (Parts A and B), CMS contracts with regional intermediaries called Medicare Administrative Contractors (MACs) to process claims and handle day-to-day administration.

When you enroll in a Medicare Advantage plan, you are signing up with a private insurer — UnitedHealth, Humana, Anthem, or another company — but that plan must follow CMS rules about what it covers, how much you pay out of pocket, and how it handles appeals. CMS audits these plans and can penalize or remove them if they do not meet federal standards.

This means you may interact with a private insurance company more often than with CMS itself, but CMS is the entity that set the terms of your coverage and has the authority to enforce them.

What CMS decides and what it does not

CMS decides which services and drugs Medicare covers, how much it pays providers for those services, and what you pay as a beneficiary. The agency also sets enrollment important date, determines which plans can offer Medicare Advantage, and oversees the appeals process if your claim is denied.

CMS does not decide whether you are old enough or disabled enough to may have access to for Medicare in the first place — that information is made by Social Security Administration (SSA) for age-based may be able to access and by SSA or the Railroad Retirement Board for disability-based may be able to access. Once you are enrolled, CMS manages your benefits.

If you disagree with a coverage decision — for example, if Medicare denies a treatment your doctor recommended — you file an appeal with CMS or its contractor, not with Social Security. This is an important distinction because the two agencies handle different parts of the Medicare system.

CMS regional offices and how to contact them

CMS operates 10 regional offices across the United States, each overseeing Medicare administration in several states. These offices handle complaints, monitor plan performance, and coordinate with state Medicaid agencies. You do not usually contact a regional office directly — instead, you reach CMS through its national helpline or website.

The main contact point for beneficiaries is 1-800-MEDICARE (1-800-633-4227), which is staffed by CMS contractors who can answer questions about your coverage, help you understand your bills, and direct you to appeals resources. You can also visit Medicare.gov, which is maintained by CMS and contains your account information, plan options, and coverage details.

If you need to file a formal complaint about a plan or a coverage decision, you can do so through Medicare.gov or by contacting your state's insurance commissioner, who works with CMS on oversight.

The role of Medicare Administrative Contractors

For Original Medicare (Parts A and B), CMS contracts with regional companies called Medicare Administrative Contractors (MACs) to process your claims, pay providers, and handle some appeals. There are 12 MAC regions in the United States, and each one covers a specific geographic area. When you submit a claim or your provider bills Medicare, it goes to the MAC for your region.

MACs are private companies — Noridian, Palmetto, Anthem, and others — but they work on behalf of CMS and must follow CMS rules. If you have a question about a claim or want to appeal a denial, the MAC is often your first contact, though you can also appeal directly to CMS if you are not satisfied with the MAC's decision.

Knowing which MAC covers your area can help you track down answers faster. You can find your MAC on Medicare.gov by entering your ZIP code.

How CMS differs from private Medicare Advantage insurers

Original Medicare (Parts A and B) is a federal program run by CMS. When you enroll in Original Medicare, you are in a government program, and CMS (through MACs) handles your claims. Medicare Advantage is different — it is a private insurance plan that must follow CMS rules but is sold and managed by a private company.

This distinction matters for appeals, coverage decisions, and complaints. If you are in Original Medicare and disagree with a coverage decision, you appeal to CMS or the MAC. If you are in a Medicare Advantage plan, you appeal to the private insurer first, and only if you are unsatisfied can you escalate to CMS. The timelines and processes are different.

Both routes are legitimate Medicare coverage. CMS oversees both, but the entity you deal with day-to-day depends on which type of plan you chose.

Frequently Asked Questions

Can I contact CMS directly if my Medicare Advantage plan denies a claim?

You must appeal to your Medicare Advantage plan first. If the plan denies your appeal, you can then escalate to CMS. CMS oversees the plan and can review the decision, but the plan has the first chance to reconsider. This process usually takes 30 to 60 days depending on the type of appeal.

Is Medicare.gov run by CMS?

Yes. Medicare.gov is the official CMS website for Medicare beneficiaries. You can view your claims, compare plans, check coverage, and file complaints there. Information on Medicare.gov comes directly from CMS, not from private insurers or third-party sites.

What if I think CMS made a mistake in my coverage decision?

You can file a formal appeal through Medicare.gov or by calling 1-800-MEDICARE. You can also contact your state's insurance commissioner or file a complaint with CMS directly. CMS has an appeals process that includes multiple levels of review if you disagree with an initial decision.

Does CMS set the premiums for Medicare Advantage plans?

CMS does not set the premiums — each private insurer sets its own. However, CMS sets the payment it makes to insurers for each beneficiary, which influences what premiums insurers charge. CMS also reviews plans to make sure premiums are reasonable and can reject a plan if it believes the premium is too high.

Who do I contact if I want to switch from Original Medicare to Medicare Advantage?

You can enroll in a Medicare Advantage plan during the Annual Enrollment Period (October 15 to December 7) through Medicare.gov, by calling 1-800-MEDICARE, or by contacting the plan directly. CMS sets the enrollment rules and important date, but the plan itself processes your enrollment.

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.