Where to sign up for a Medicare supplement depends on which insurance company you choose

You sign up directly with the insurance company selling the plan, not through Medicare itself. Each company — like AARP/UnitedHealthcare, Cigna, Humana, or Blue Cross Blue Shield — has its own enrollment process. You can contact them by phone, visit their website, or work with an independent insurance agent who represents multiple companies. The agent route is often easiest because one person can show you plans from several insurers side by side, and you do not pay extra for using them.

The place you sign up matters less than when you sign up. Medicare has a limited window called the Medigap Open Enrollment Period when insurance companies must accept you without medical underwriting — meaning they cannot deny you or charge more based on your health history. This period lasts six months and starts the first day of the month you turn 65 and are enrolled in Medicare Part B. If you miss this window, companies can ask health questions and may refuse to cover pre-existing conditions.

Key Takeaways

  • Contact the insurance company directly by phone or website, or use an independent agent who can compare multiple plans at once.
  • Your six-month Medigap Open Enrollment Period begins the first day of the month you turn 65 and enroll in Medicare Part B — this is your strongest protection against denial or higher rates.
  • If you miss the open enrollment window, some states have protections that let you sign up later, but these vary widely by state and plan type.
  • Have your Medicare card and a list of current medications ready when you contact a company, because they may ask about your health.

How to find insurance companies that sell Medigap plans in your state

Medicare publishes a searchable list of insurers on Medicare.gov under "Medigap Policies." You enter your state and zip code, and the tool shows every company licensed to sell supplement plans where you live. Not all companies operate in all states, so this list tells you who is actually available to you — not a national list that might include companies that do not serve your area.

You can also call 1-800-MEDICARE (1-800-633-4227) and ask for a list of Medigap insurers in your state. The representative can read you company names and phone numbers. This is useful if you do not have internet access or prefer to work by phone from the start.

Using an independent insurance agent

An independent agent (also called a broker) represents multiple insurance companies and can show you plans from several at once. This saves you from calling five different companies separately. Agents are paid by commission from the insurance company, not by you, so there is no extra cost to use one.

To find an agent, search "Medicare supplement agent near me" or ask your doctor's office if they have recommendations. You can also contact your State Health Insurance information Program (SHIP), which is free and can connect you with local agents or answer questions directly. Find your state's SHIP by calling 1-877-839-2675 or visiting shiptalk.org.

Signing up directly with an insurance company

If you know which company and plan you want, you can skip the agent and enroll directly. Visit the company's website and look for "Medigap" or "Medicare Supplement" enrollment. Most companies let you start the process online and finish by phone, or you can call their Medicare line directly. Have your Medicare card handy and be ready to answer health questions if you are outside the open enrollment window.

When you call, confirm the plan letter (Plan A, Plan B, Plan G, and so on — these are standardized across all companies in your state), the monthly premium, and the effective date. Ask whether the company will send you a confirmation letter and when coverage begins. Some plans start the first of the month after you sign up; others may have a later start date.

What happens after you sign up

Once you enroll, the insurance company sends you a policy document and an insurance card. Your coverage usually starts on the first of the month following your enrollment, though some companies offer earlier start dates. You will receive bills from the insurance company (not Medicare) for your monthly premium, separate from your Medicare Part B premium.

Your supplement plan works alongside Medicare Part A and Part B. When you see a doctor or go to the hospital, Medicare pays its share first, then your supplement plan pays the costs Medicare does not cover — up to the limits of your specific plan. You do not file claims yourself; the providers bill Medicare and the insurance company directly.

If you miss the open enrollment window

Missing the six-month window does not automatically close the door, but your options narrow. Some states have may provide issue rights that let you sign up for certain plans without medical underwriting in specific situations — for example, if you lose employer coverage or move to a new state. Other states have no may provide issue protection at all.

If you missed the window and do not may have access to for may provide issue in your state, insurance companies can deny you or charge more based on health conditions. Some companies are more willing to take late enrollees than others, so it is worth calling several. Your State Health Insurance information Program can tell you what protections exist in your state and which companies are most likely to work with you.

Frequently Asked Questions

Can I sign up for a Medigap plan online?

Most companies let you start the process online, but you will likely need to finish by phone or mail to complete enrollment. Some insurers offer fully online enrollment. When you contact a company, ask whether you can complete the entire process without calling.

What if I want to switch from one Medigap plan to another?

You can switch plans at any time, but the new company can ask health questions unless you are within your open enrollment window or may have access to for may provide issue. Switching is easiest during your initial six-month period. After that, contact your current insurer to find out their rules for switching to a different plan letter.

Do I need to sign up for a Medigap plan, or is it optional?

Medigap is optional. If you do not buy a supplement plan, you are responsible for the costs Medicare does not cover — deductibles, coinsurance, and copays. Many people find a supplement plan worth the monthly premium because it protects them from large unexpected bills.

What if I already have health insurance through my job?

If you have retiree coverage or are still working, you may not need a Medigap plan right away. However, if you lose that coverage later, you may not may have access to for Medigap without medical underwriting. Talk to your employer's benefits office about how losing coverage affects your future Medigap options.

Can I sign up for Medicare Part D (prescription drug coverage) at the same time as Medigap?

Yes. You can enroll in a Medigap plan and a Part D plan during the same period. Some people use an agent who handles both, or you can sign up with separate companies. Part D enrollment happens through Medicare or private insurers, separate from your Medigap sign-up.