Medicare Supplement Insurance Enrollment

05.12.2025

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Medicare costs vary depending on the type of services you receive and the coverage you choose. Medicare supplement insurance is one of those coverage options. Let’s take a closer look at this type of insurance and the enrollment process for it, so you can better understand your options.

What Is Medicare Supplement Insurance?

Medicare Supplement insurance is a private insurance policy designed to work alongside Original Medicare. It helps cover some of the out-of-pocket costs that Original Medicare doesn’t fully cover. Depending on the plan you choose, this may include things like:

  • Part A coinsurance and hospital costs
  • Part A deductible
  • Part B coinsurance or copayments
  • Blood (first 3 pints)
  • Hospice care coinsurance
  • Skilled nursing facility care coinsurance
  • Foreign travel emergency care (up to plan limits)

To ensure consistency, the government standardizes these plans, assigning letter designations, like Plan G or Plan N. (In Massachusetts, Minnesota and Wisconsin, plans are standardized in a different way). This standardization means that a Plan G, for example, offers the same core benefits regardless of the insurance company or your location.1

What Is Medicare Supplement Open Enrollment?

Your Medicare Supplement Open Enrollment1 is a one-time period that begins the first month you have Medicare Part B and you’re 65 or older. It lasts six months. (In some states, this open enrollment period is called a guaranteed issue enrollment period). For example, if your Medicare Part B coverage starts on July 1 and you’re 65, your Medicare Supplement Open Enrollment would end on December 31.

Medicare Supplement Open Enrollment vs Underwriting

During your six-month Medicare Supplement Open Enrollment Period, you can enroll for the first time or switch plans and insurers can’t deny you coverage for any health issues you may have. This is also known as a guaranteed issue period. After your Open Enrollment Period, you may be subject to underwriting. That’s when insurers ask you questions about your health status. As a result, you may be denied certain plans, or it may cost more based on your health.

Can You Enroll in a Medicare Supplement Insurance Plan If You Have Medicare Advantage?

No, you can’t purchase Medicare Supplement coverage if you have Medicare Advantage. If you have a Medicare Advantage plan, you will first need to switch to Original Medicare before you can enroll in a Medicare Supplement plan. You will need to do so during the Annual Enrollment Period (Oct. 15–Dec. 7) or the Medicare Advantage Open Enrollment Period, which ranges from Jan. 1–Mar. 31. If you switch to Medicare Supplement, you may be subject to underwriting.2

If you have Medicare Advantage, you may also qualify for a Special Enrollment Period when you have other events happen in your life, such as moving or losing coverage. In these cases, you may not be subject to underwriting for a Medicare supplement plan.

Enrollment Process for Medicare Supplement Plans

Your Medicare Supplement Open Enrollment Period is generally the best time to apply, but other enrollment opportunities may be available. Explore all potential enrollment periods and guaranteed issue rights to maximize your options. To sign up, choose a plan offered by a private insurance company and submit an application.

Can You Enroll in Medicare Supplement Plans at Any Time?

After your guaranteed issue Open Enrollment Period, you can apply for a Medicare Supplement policy at any time, but you may be subject to underwriting and your approval is not guaranteed.

Steps to Sign Up for Medicare Supplement Coverage

To sign up for Medicare Supplement coverage, you’ll need to research and apply directly with your chosen insurer. Here’s a more detailed breakdown of the process:

  1. Confirm eligibility: Ensure you are enrolled in Medicare Part A and Part B. Verify that you are not enrolled in a Medicare Advantage Plan, as you cannot have both a Medicare Supplement plan and a Medicare Advantage plan simultaneously.
  2. Choose a plan: Compare Medicare supplement plans (Plan G, Plan N, etc.) based on their coverage, costs (premiums, deductibles), and your individual healthcare needs. Consider factors like your health status, anticipated medical needs, and budget.
  3. Select an insurer: Research private insurance companies offering Medicare supplement plans in your area. Compare insurers based on their financial strength, premium rates, and customer service ratings.
  4. Gather required information: Collect necessary information, including your Social Security number (SSN), Medicare Part A and Part B enrollment dates, and your Medicare Beneficiary Identifier (MBI) from your Medicare card. Be prepared that some health information may be requested, especially if you are not enrolling during your Medicare Supplement Open Enrollment guaranteed issue period or other guaranteed issue period.
  5. Submit application:

    6. You can enroll through various methods:

    • Online: Many insurers offer online applications.
    • By phone: Have a licensed insurance agent take your application over the phone.
    • With an agent: Work with a local licensed insurance agent who can assist you with the application process.
  6. Await approval: The application review time varies. During your Medicare Supplement Open Enrollment Period or under guaranteed issue rights, approval is typically faster, often within 24 hours. If you apply outside these periods, the insurer may underwrite your application, which can extend the review process as they assess your health history. If your application is underwritten, a decision to approve or decline your coverage may take a few days.

Choosing the Right Medicare Supplement Plan

When choosing a Medicare Supplement plan, review the coverage offered and determine what is most important to you. Consider things like:

  • Cost – Plans may vary in monthly premiums, annual deductibles, and other out-of-pocket expenses. Determine how you want to balance these two options.
  • Service coverage – Plans differ in what services and how much they cover. For instance, some plans cover foreign travel emergencies and others don’t. Consider the medical services you may need and how the plan addresses those.
  • Medical needs – Think about any of your current medical conditions and treatments and how the plan would cover those.

Tips for Selecting Supplemental Medicare Insurance

In addition to evaluating your coverage needs, here are a few more tips to consider to when selecting a Medicare supplement plan:

  • Review carriers’ stability and customer service: Carriers can vary in their level of reliability and the quality of their customer service teams.
  • Consider the timing of enrollment: Understand the benefits of enrolling during your Medicare Supplement Open Enrollment Period or guaranteed issue period to avoid potential medical underwriting and higher premiums.
  • Explore technological accessibility: Check insurers’ online capabilities to ensure it meets your needs for accessing policy information, claims processing, and customer support.

Understanding Medicare Supplement insurance

Understanding important factors like enrollment periods, underwriting requirements and plan types can help you know what to expect with Medicare supplement insurance.

The Mutual of Omaha Medicare Advice Center can help further boost your understanding. Answer a few simple questions, and it will help assess your coverage preferences.

Frequently Asked Questions on Medicare Supplement Enrollment

    1. What documents do I need for Medicare Supplement enrollment?

      For Medicare Supplement enrollment, have your Medicare card or MBI, and Part A and B enrollment dates ready. Provide personal details like your date of birth and contact information. If applicable, gather spouse/partner information for potential discounts. Outside your open enrollment period or guaranteed issue periods, health and medication details may be required. Insurers use this information to process your application and determine eligibility.

    2. What if I miss the Medicare Supplement Open Enrollment Period?

      You’ll still be able to apply, but your approval is not guaranteed. You may have a higher premium or may be denied coverage.

    3. Can I delay Medicare while working and keep the guaranteed issue right when I retire?

      If you are working after you turn 65 and have group health coverage, you may want to wait to enroll in Part B. When your group coverage ends, you can enroll in Part B. Your Medicare supplement Open Enrollment Period will begin then and you will be able to enroll in any plan without consideration of your health issues.

    4. Can I switch Medicare Supplement plans later?

      Yes, switching Medicare Supplement plans is possible. Guaranteed issue rights allow you to switch without health considerations under specific conditions.3 Even outside these periods, you can apply for a new plan, though medical underwriting may apply.

1 Medicare.gov. Web page: Get Medigap Basics. Retrieved February 28, 2025, from https://www.medicare.gov/health-drug-plans/medigap/basics

2Medicare.gov. Fact Sheet: Understanding Medicare Advantage & Medicare Drug Plan Enrollment Periods. Retrieved Feb. 28, 2025, from https://www.medicare.gov/publications/11219-Understanding-Medicare-Advantage-Medicare-Drug-Plan-Enrollment-Periods.pdf

3Medicare.gov. Web page: Can I change my Medigap policy? Retrieved on Feb. 6, 2025, from https://www.medicare.gov/health-drug-plans/medigap/ready-to-buy/change-policies

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