Who Regulates Medicare Supplement Plans? Federal Law, CMS, the NAIC and Your State

Reviewed by Russell Noga, Licensed Medicare Insurance Broker (all 50 states) — Last updated November 7, 2026

Your Medicare card is federal. Your Medicare Supplement policy is not. It’s private insurance, bought from a private company, and most of the day-to-day oversight sits in a state office few people ever call until something goes wrong.

That split explains a lot of confusion. People phone Medicare about a premium jump, and Medicare can’t help. People assume a state can freeze rates, and it usually can’t. This page maps who holds which lever, where to file a complaint, how to look up the paperwork behind your premium, and what a regulator can and can’t do for you.

Think of Medigap oversight as a floor and a building. Congress and CMS pour the floor: minimum benefits, standardized plan letters, sales protections and loss-ratio minimums that apply nationwide. The states build on top of it. They license the companies and the agents, approve the policy forms, review premium filings and answer consumer complaints.

Before 1980, states did all of it alone. A Congressional Research Service history of Medigap describes that period as one with no federal standards at all, which is why the federal layer exists. Even now, CRS calls regulation primarily a state responsibility. Federal law mostly tells each state what its rules must include, then leaves the enforcement to the state insurance commissioner.

Every federal Medigap rule traces back to section 1882 of the Social Security Act, codified at 42 U.S.C. 1395ss. It has been rewritten several times, and each change still shapes what you can buy today:

Section 1882 also makes certain sales practices federal violations, which matters for the complaint section below.

The Centers for Medicare & Medicaid Services administers Medicare, but its Medigap job is narrow. It publishes the standardized benefit rules, writes the annual “Choosing a Medigap Policy” guide and recalculates the high-deductible amount each year using the consumer price index. That figure, $3,050 for 2027, applies to the high-deductible versions of Plans F and G; our page on High-Deductible Plan F shows what it means for a policyholder’s yearly costs.

What CMS doesn’t do is price your policy. The federal guide says each insurance company decides how it sets its premium, and it sends readers with policy questions to their State Insurance Department, not to 1-800-MEDICARE. Nor does CMS license agents or pay any part of a Medigap premium.

The National Association of Insurance Commissioners is a standard-setting group made up of the chief insurance regulators of each state, not a federal agency. Its Medicare Supplement Insurance Minimum Standards Model Act (Model 650) and the regulation that carries it out (Model 651) are the text most states adopt, sometimes word for word, as their own Medigap law.

Federal law leans on these models directly. The plan letters, the benefit chart and the outline-of-coverage format you see when shopping come from the NAIC regulation, which Congress tied to section 1882. When the rules change, the NAIC amends the model, and CMS publishes notice of the change in the Federal Register. The NAIC also runs SERFF, the electronic system insurers use to send rate and form filings to the states, and it publishes a yearly chart of state-approved “new or innovative” benefits.

Once a company wants to sell Medigap in a state, the state’s insurance department is its regulator. The table lines up each layer against the decisions people actually ask about:

Sources: Social Security Act §1882; CMS “Choosing a Medigap Policy”; NAIC Models 650 and 651.

States can also go beyond the federal floor. That’s why some have yearly switching rights or under-65 rules; our state-by-state guaranteed issue chart collects them.

Every state reviews Medigap rates, but the process varies more than most guides admit. Three state laws show the range:

Sources: NY DFS Medicare supplement rate filing instructions; Conn. Gen. Stat. §38a-474; Rev. Code Wash. §48.66.035. Rules in your state may differ, so check its insurance department’s site.

To read a filing yourself, use SERFF Filing Access, the NAIC’s public portal, which links to filing searches for most states. Search by the insurer’s legal company name, not its brand.

Here’s a hypothetical increase moving through a prior-approval state that follows New York’s timeline. The dollar figures are an illustration, not a real filing.

An insurer’s block of Plan G policies has paid out more in claims than projected. About 150 days before the policy anniversary, it files a request for a 12% increase, with actuarial exhibits showing the block’s loss ratio. Policyholders get an initial notice and a 30-day window to send comments. Regulators check whether the higher premium still meets the minimum loss ratio and whether the claims data supports it. Suppose they approve 8% instead.

At least 60 days before the anniversary, each policyholder gets written notice of the approved change. On a $200 monthly premium, the requested 12% would have added $24 a month, or $288 a year. The approved 8% adds $16 a month, or $192 a year, so the new bill is $216.

The process can trim a request, but it rarely stops one when claims really did rise. For what to do once the notice arrives, see our guide to Medicare Supplement rate increases.

Where to go depends on what went wrong:

Know the limits too. A state can make an insurer justify a rate, cut a request or deny one that fails the loss-ratio test. It generally can’t stop an increase the claims data supports, set your price below that, or force a company to accept you outside your open enrollment or a guaranteed issue right. For a full overview of the plan letters themselves, start with our guide to Medicare Supplement plans.

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