What the Centers for Medicare and Medicaid Services Does and Why It Matters to You

The Centers for Medicare and Medicaid Services runs Medicare, Medicaid, and the Children's Health Insurance Program

The Centers for Medicare and Medicaid Services (CMS) is the federal agency inside the U.S. Department of Health and Human Services that administers Medicare, Medicaid, and the Children's Health Insurance Program (CHIP). It does not provide the insurance itself — it sets the rules, pays the claims, and oversees the doctors, hospitals, and insurance companies that do the actual work.

When you turn 65 and enroll in Medicare, CMS is the organization that processes your enrollment, determines what you pay, and tells Medicare Advantage plans and Medigap insurers what they can and cannot charge you. When you call Medicare with a question about your benefits or your bill, you are calling a contractor that works for CMS. When your doctor submits a claim, CMS (or a contractor working on its behalf) decides whether to pay it.

CMS also runs the state Medicaid programs — the insurance for people with lower incomes — though each state has some freedom to set its own rules within federal guidelines. The same is true for CHIP, which covers children in families that earn too much for Medicaid but not enough to afford private insurance.

Key Takeaways

• CMS is a federal agency that sets rules and pays claims for Medicare, Medicaid, and CHIP, but does not directly provide insurance or see patients.
• Medicare enrollment, billing questions, and claim decisions all go through CMS or its contractors, not through a separate private company.
• CMS publishes the rules that govern what Medicare covers, what you pay, and what doctors and hospitals can charge.
• Each state runs its own Medicaid program under CMS oversight, so benefits and rules vary by state.
• CMS maintains databases of doctors, hospitals, and nursing homes, along with their quality ratings and payment histories.

What CMS Actually Does Day to Day

CMS processes millions of claims every month. When your doctor bills Medicare for an office visit, a CMS contractor reviews the claim to check that the service was covered, that the price was reasonable, and that your doctor is enrolled in Medicare. If everything checks out, CMS pays the doctor and sends you an explanation of benefits. If something is wrong, CMS denies the claim and tells your doctor why.

CMS also sets the payment rates that Medicare pays doctors and hospitals. These rates change every year and vary by location and type of service. A knee replacement in rural Montana costs Medicare a different amount than the same surgery in New York City, and CMS publishes those rates publicly so doctors and patients can see them.

Beyond claims, CMS collects data on how well doctors and hospitals perform. It publishes quality ratings on its website so you can compare hospitals by infection rates, readmission rates, and patient satisfaction. It also maintains the list of providers enrolled in Medicare — if a doctor or nursing home is not on that list, Medicare will not pay for their services.

How CMS Differs from Private Insurance Companies

CMS is not an insurance company. It does not employ doctors, own hospitals, or sell policies. Instead, it is a government agency that runs a government insurance program. This means it follows federal law and federal budget rules, not shareholder profit targets.

Private Medicare Advantage plans and Medigap insurers operate under CMS rules and oversight. CMS tells them what benefits they must offer, what they can charge, and how they must handle complaints. CMS also audits their claims and their customer service. If a plan breaks the rules too often, CMS can fine it or remove it from the Medicare program.

The same structure applies to Medicaid. CMS sets the federal rules, but each state runs its own Medicaid program and hires its own contractors to process claims. This is why Medicaid benefits differ from state to state — CMS sets a floor, but states can build higher.

Where to Find CMS Information and Tools

CMS publishes most of its information on Medicare.gov, which is the official Medicare website. There you can search for doctors and hospitals, compare Medigap and Medicare Advantage plans, check your claims, and read the official Medicare handbooks. You can also create an account to view your personal Medicare information, including your claims history and what you have paid toward your deductible.

CMS also runs Care.cms.gov, which is a separate site focused on quality data. There you can search for nursing homes, dialysis centers, and home health agencies and see their inspection results and quality ratings. This site is useful if you are looking for a facility or want to understand how your current provider is rated.

For Medicaid, CMS does not run a single website because each state runs its own program. Your state Medicaid office has its own website and phone number. You can find your state's Medicaid contact information through the CMS website or by calling 1-800-MEDICARE.

How CMS Rules Affect Your Out-of-Pocket Costs

CMS sets the rules that determine what you pay for Medicare. It decides what the Part B premium is, what the deductible is, and what the coinsurance percentages are. Every year, CMS announces these amounts, and they often change. The Part B premium, for example, has risen most years, though the amount varies based on Social Security cost-of-living adjustments and Medicare trust fund balances.

CMS also sets rules about what Medicare covers and what it does not. If your doctor wants to order a test or procedure, Medicare coverage depends on CMS rules about whether that service is medically necessary and whether it is covered at all. Your doctor can appeal a CMS denial, and you can appeal it too, but the rules come from CMS.

For people on Medicaid, CMS sets minimum coverage requirements, but your state can cover more. Some states cover dental care, vision care, and hearing aids; others do not. Your state Medicaid office decides, within CMS guidelines.

Understanding CMS Contractors and Who You Actually Call

When you call Medicare with a question, you are usually calling a CMS contractor, not CMS itself. CMS hires private companies to handle customer service, process claims, and handle appeals. These contractors work under CMS rules and oversight, but they are the ones answering the phone and making day-to-day decisions.

There are different contractors for different regions and different types of claims. If you have a question about a doctor's bill, you might call one contractor. If you have a question about a hospital bill, you might call another. Medicare.gov tells you which contractor handles your area and what their phone number is.

This structure can be confusing because you may not know whether you are talking to CMS or a contractor. From your perspective, it does not matter much — both are bound by the same federal rules. But if you need to file a formal appeal or complaint, knowing which contractor handled your claim can help you send your paperwork to the right place.

Frequently Asked Questions

Is CMS the same as Medicare?

No. CMS is the federal agency that runs Medicare. Medicare is the insurance program itself. CMS sets the rules and pays the claims, but Medicare is what covers your health care costs. Think of CMS as the organization and Medicare as the program it manages.

Can I contact CMS directly with a problem?

You can reach CMS through Medicare.gov or by calling 1-800-MEDICARE. Most questions are handled by CMS contractors, not by CMS staff directly. If you have a formal complaint about how CMS is running the program, you can file it through Medicare.gov, but routine questions go to contractors first.

Does CMS decide whether my doctor is in-network?

CMS maintains the list of doctors enrolled in Medicare, but whether a doctor is "in-network" depends on your specific plan. If you have Original Medicare, all enrolled doctors are in-network. If you have a Medicare Advantage plan, that plan decides which doctors are in-network. CMS oversees both, but the plan makes the network decision.

Why do Medicare rules change every year?

CMS updates Medicare rules and payment rates annually based on changes in health care costs, inflation, and federal budget law. Congress also passes laws that change Medicare rules. These changes are published in the Federal Register and announced on Medicare.gov, usually in the fall for changes that take effect January 1.

What should I do if I disagree with a CMS decision about my claim?

You have the right to appeal any Medicare claim denial. The appeal process has multiple levels: you can ask the contractor to reconsider, then request a hearing before an administrative law judge, then appeal to the Medicare Appeals Council. Instructions for each step are on your explanation of benefits or on Medicare.gov.