The Core Facts About Medicare Supplement Open Enrollment

Medicare Supplement open enrollment is a six-month window that begins the month you turn 65 and enroll in Medicare Part B. During this period, insurance companies must sell you a Medigap policy at the lowest available rate, without medical underwriting — meaning they cannot deny you, charge you more, or exclude pre-existing conditions. This window is the only time most people can buy Medigap without answering health questions or facing waiting periods.

Once this six-month period ends, you enter what is called the "general enrollment" period. After that point, insurers can reject your process, charge you substantially more based on your health history, or impose waiting periods of up to six months for pre-existing conditions. The difference in cost and access between buying during open enrollment and buying later can be thousands of dollars over time.

The open enrollment period applies only to Medigap policies, not to Medicare Advantage plans. It also does not explore if you already have Medigap coverage — the protection is designed for people new to Medicare.

Key Takeaways

  • Open enrollment for Medigap lasts six months, starting the month you turn 65 and enroll in Medicare Part B.
  • During open enrollment, insurers cannot deny you, charge you more based on health, or exclude pre-existing conditions.
  • After open enrollment ends, insurers can reject your process, charge higher premiums, or impose waiting periods for pre-existing conditions.
  • You must enroll in Medicare Part B to start the open enrollment clock — turning 65 alone does not trigger it.
  • This protection applies only to Medigap policies, not to Medicare Advantage or other Medicare plan types.

When Your Open Enrollment Period Starts and Ends

Your six-month window begins on the first day of the month you turn 65, provided you have already enrolled in Medicare Part B. If you turn 65 on March 15, your open enrollment begins March 1. If you enroll in Part B after turning 65 — for example, at age 66 — your open enrollment begins the month you enroll in Part B, not the month you turned 65.

The window closes at the end of the sixth calendar month. If you turn 65 in March, your open enrollment runs through August 31. If you enroll in Part B in October at age 67, your open enrollment runs through March 31 of the following year. After the last day of that sixth month, the open enrollment protection ends.

Timing matters because you cannot get it back. If you miss the window by even one day, you lose the right to buy Medigap without medical underwriting. Some people delay enrolling in Part B to avoid the Part B premium, but this also delays the start of open enrollment — a choice that can cost far more in higher Medigap premiums later.

What Happens If You Miss Your Open Enrollment Window

After open enrollment ends, you can still buy a Medigap policy, but the rules change. Insurers can require you to answer detailed health questions and can deny you based on your answers. They can also charge you a higher premium — sometimes 25 to 50 percent more than someone who bought during open enrollment. Some insurers will not sell to you at all if you have certain health conditions.

Additionally, if you have a pre-existing condition, the insurer can impose a waiting period of up to six months before that condition is covered. This means you could pay premiums for six months and still have no coverage for the condition you most need help with.

A few states have additional protections that extend limited enrollment rights beyond the federal six-month window, but these vary widely and do not explore everywhere. You cannot count on state protections to rescue you if you miss the federal window.

How Open Enrollment Differs From Other Medicare Enrollment Periods

Medicare has several enrollment periods, and they work differently. The Initial Enrollment Period for Part A and Part B is seven months long and centers on the month you turn 65. The Annual Enrollment Period (also called the Open Enrollment Period for Medicare Advantage and Part D) runs from October 15 to December 7 each year and lets you switch between Medicare Advantage plans or change your prescription drug coverage.

The Medigap open enrollment period is separate from both of these. It is not the same as the Annual Enrollment Period, and it does not repeat every year. You get it once, at the beginning of your Medicare life. If you miss it, you do not get another automatic window unless you move to a different state or experience certain may have access to events.

This is why the Medigap open enrollment period is often called the most important enrollment window in Medicare. The other periods come around every year, but this one does not.

What You Can and Cannot Do During Open Enrollment

During open enrollment, you can buy any Medigap plan that your state allows, from any insurer that sells Medigap in your state. You can switch between plans, and you can buy multiple policies if you choose (though this is not recommended, as you will pay multiple premiums). Insurers must accept you at the standard rate with no medical questions.

You cannot, however, use open enrollment to buy Medicare Advantage coverage. Open enrollment applies only to Medigap policies — the ten standardized plans labeled A through N. If you want Medicare Advantage, you have different enrollment windows and different rules.

You also cannot use open enrollment to buy a Medigap policy if you already have one. The protection is designed for people new to Medicare. If you already have Medigap and want to switch to a different plan, you may face medical underwriting depending on your state and the circumstances of the switch.

Steps to Take Before Your Open Enrollment Ends

First, confirm the exact end date of your window. Count six months forward from the first day of the month you enrolled in Part B. Write down that date and set a reminder for two weeks before it.

Second, compare the Medigap plans available in your state. The plans are standardized — Plan A covers the same things regardless of which insurer sells it — but premiums vary widely. Use the Medicare.gov Plan Finder tool or contact insurers directly for quotes. Get at least three quotes for each plan you are considering.

Third, decide which plan fits your needs and budget. Plans with higher premiums cover more out-of-pocket costs, but the lowest-premium plan may be right for you if you are healthy and want to minimize monthly payments. There is no single "best" plan.

Fourth, buy the plan before your open enrollment ends. Do not wait until the last week. Submit your process at least two weeks early to allow time for processing. Once you receive confirmation that your policy is in force, you are protected.

Frequently Asked Questions

Does turning 65 automatically start my open enrollment, or do I have to enroll in Part B first?

You must enroll in Medicare Part B to start the clock. Turning 65 alone does not trigger open enrollment. If you delay enrolling in Part B, your open enrollment period does not begin until the month you actually enroll in Part B.

Can I use my open enrollment period to buy Medicare Advantage instead of Medigap?

No. Open enrollment applies only to Medigap policies. Medicare Advantage has its own enrollment rules and windows. If you want Medicare Advantage, you have different important date and protections.

What if I already have health insurance from my job when I turn 65?

You still have a Medigap open enrollment period once you enroll in Medicare Part B. Your employer coverage does not extend or replace this window. If you leave your job and lose that coverage, you will need Medigap or Medicare Advantage, and your open enrollment period may have already ended.

Can I buy Medigap after my open enrollment ends if I am willing to pay more?

You may be able to, but the insurer can deny you, charge you significantly more, or impose waiting periods for pre-existing conditions. Some insurers will not sell to you at all. There is no may provide you will be able to buy coverage at any price after open enrollment ends.

If I move to a different state, do I get another open enrollment period for Medigap?

Some states have limited protections for people who move, but these vary. A few states allow a new enrollment period if you move into their state. Contact your new state's insurance commissioner's office to learn what protections explore where you are moving.