You can buy a Medicare Supplement during certain windows, but not whenever you want

Medicare Supplement insurance (also called Medigap) has open enrollment periods when you can buy a policy without restrictions. Outside those windows, insurers can deny you coverage, charge you more, or exclude pre-existing conditions from what they will pay for. The timing depends on when you first became may be able to access for Medicare and whether you already have coverage.

The most important window is your Initial Enrollment Period, which lasts six months and starts the month you turn 65 and enroll in Medicare Part B. During this period, you can buy any Medigap policy sold in your state, and insurers cannot turn you down or charge more based on your health history. If you miss this window, buying a policy later becomes harder and more expensive.

Key Takeaways

  • Your Initial Enrollment Period for Medigap runs for six months starting the month you turn 65 and sign up for Medicare Part B, and this is the easiest time to buy.
  • If you miss your Initial Enrollment Period, you can still buy during the annual Open Enrollment Period (October 15 to December 7), but insurers can reject you or charge more based on health conditions.
  • Some states have additional protections that let you switch or buy Medigap outside the standard windows, so check your state's rules.
  • If you had employer or union coverage when you turned 65, you may have a separate enrollment window after that coverage ends.
  • Waiting to buy Medigap after your Initial Enrollment Period closes can cost hundreds of dollars more per year in premiums.

Your Initial Enrollment Period: The six-month window that matters most

Your Initial Enrollment Period begins the first day of the month you turn 65, as long as you are enrolled in Medicare Part B. It runs for exactly six months. During this time, you can purchase any Medigap plan offered in your state, and the insurance company must accept you regardless of your health. They cannot charge you more because you have diabetes, heart disease, or any other condition.

This window closes at the end of the sixth month. If you turn 65 in March and enroll in Part B that month, your period runs through August. Once September arrives, the protections end. After that date, insurers can review your medical history and decide whether to sell you a policy at all.

The reason this period exists is federal law. Congress created it to prevent people from being locked out of coverage straightforward because they waited. But the protection is time-limited, so missing it has real consequences.

Open Enrollment Period: October 15 to December 7 each year

Every year, there is a second window called the Open Enrollment Period for Medigap. It runs from October 15 through December 7. During these weeks, you can buy or switch Medigap policies without medical underwriting — meaning the insurer cannot reject you based on health conditions or charge you more for pre-existing illnesses.

This annual window is available to anyone with Medicare Part A and Part B, whether or not you missed your Initial Enrollment Period. However, it only lasts about seven weeks, and it happens at the same time every year. If you do not buy during this window, you will need to wait until the next October 15.

One important limit: during Open Enrollment, you can usually switch from one Medigap policy to another, but you cannot necessarily buy a new Medigap policy if you do not already have one. Rules vary by state. Check with your state's insurance commissioner's office or call 1-800-MEDICARE to learn what your state allows.

What happens if you buy outside these windows

If you try to buy Medigap outside your Initial Enrollment Period or the annual Open Enrollment Period, the insurance company can underwrite your process. This means they will review your medical history, ask detailed health questions, and decide whether to accept you. They can also charge you a higher premium based on your age and health status — a practice called medical underwriting.

In some cases, insurers will deny your process entirely. They may also exclude coverage for a condition you already have, meaning they will not pay for treatment related to that illness for a set period (often six months to a year). These exclusions are called pre-existing condition limitations, though not all states allow them.

The financial impact can be substantial. A policy bought outside the protected windows can cost 25 to 50 percent more per month than one bought during your Initial Enrollment Period, depending on your age and health. Over several years, this difference adds up to thousands of dollars.

Special enrollment periods for people with employer coverage

If you were covered by a health plan through your job or your spouse's job when you turned 65, you may have a different timeline. Federal law gives you a special enrollment period that begins when that employer coverage ends. You have up to 63 days after the coverage stops to buy Medigap without medical underwriting.

This rule protects people who stayed on employer plans instead of buying Medigap at 65. However, you must have been enrolled in both Medicare Part A and Part B during the time you had the employer coverage. If you delayed enrolling in Part B, this special period may not explore to you.

If you had union coverage or retiree health benefits, the same rule usually applies. The key is that your employer or union coverage must have been primary (meaning it paid first), and you must have had Medicare at the same time.

State-specific rules that may give you more options

Some states have passed their own laws that create additional enrollment windows or protections beyond the federal rules. For example, a few states allow you to buy Medigap during a window after you turn 65, even if you did not enroll in Part B right away. Other states let you switch between Medigap policies more freely than federal law requires.

Because these rules vary significantly by state, you need to check with your state's insurance commissioner's office or your state health insurance counseling program. You can find your state program by calling 1-800-MEDICARE and asking for the State Health Insurance information Program (SHIP) in your area. SHIP counselors can tell you exactly what windows are available to you based on where you live and your situation.

A few states also have rules about how much insurers can charge for Medigap based on age. Some use "community rating," meaning everyone pays the same price regardless of age. Others use "issue-age rating," where your premium is based on your age when you buy. Still others use "attained-age rating," where your premium goes up as you get older. These pricing rules affect how much you will pay, so it is worth understanding your state's approach.

What to do if you missed your Initial Enrollment Period

If you did not buy Medigap during your six-month Initial Enrollment Period, you are not without options, but your choices are narrower and more expensive. Your next may provide window is the annual Open Enrollment Period from October 15 to December 7. Mark those dates on your calendar and contact insurers in your state during that window.

In the meantime, check whether your state has special rules that might help. Some states allow people who missed their Initial Enrollment Period to buy Medigap during a separate state-run window. Call your state insurance commissioner's office or SHIP to ask.

If you need coverage before October and your state does not have a special window, you can explore to insurers outside the protected periods, but understand that they can deny you or charge more. Some people in this situation choose to wait for October rather than pay the higher rates. Others explore anyway and accept the higher cost to get coverage sooner. There is no single right answer — it depends on your health, your budget, and how long you can wait.

Frequently Asked Questions

Can I buy Medigap if I am already on Medicare Advantage?

You can buy Medigap, but timing matters. If you are switching from Medicare Advantage to Original Medicare (Part A and Part B), you have a 63-day window from the date your Medicare Advantage coverage ends to buy Medigap without medical underwriting. After that window closes, insurers can review your health. Check with your state program to confirm the exact rules where you live.

What if I turned 65 but did not enroll in Part B right away?

Your Initial Enrollment Period for Medigap starts when you enroll in Part B, not when you turn 65. So if you delayed Part B enrollment, your six-month Medigap window starts later. However, delaying Part B itself can trigger Medicare penalties, so talk to someone at 1-800-MEDICARE before you delay either enrollment.

Can I switch Medigap policies during Open Enrollment?

Yes. During the annual Open Enrollment Period (October 15 to December 7), you can switch from one Medigap policy to another without medical underwriting. However, if you do not already have a Medigap policy, whether you can buy a new one during Open Enrollment depends on your state's rules. Contact your state insurance commissioner's office to confirm.

Does my age affect the price if I buy outside the protected windows?

Yes. Outside your Initial Enrollment Period and Open Enrollment, insurers can charge you more based on your age and health. How much more depends on your state's rating rules and the insurer's underwriting. Prices can be 25 to 50 percent higher than what you would have paid during your Initial Enrollment Period.

What is the difference between Medigap and Medicare Advantage?

Medigap is supplemental insurance that works alongside Original Medicare (Part A and B) to cover costs Medicare does not pay. Medicare Advantage is an alternative to Original Medicare — it is a different type of plan run by private insurers. You cannot have both at the same time. If you have Medicare Advantage and want to switch to Original Medicare with Medigap, you have a 63-day window to buy Medigap without medical underwriting.