Medicare Supplement Insurance, or Medigap, is health insurance that covers “gaps” in Medicare Part A and Part B coverage. Although you use your Medigap policy with Original Medicare, Medigap has its own rules for when and how you can sign up.

The Medigap open enrollment period is the easiest and least expensive opportunity to enroll in Medicare Supplement Insurance. If you miss your Medigap open enrollment period, you might end up spending much more for Medicare Supplement Insurance or even be unable to buy a plan.

Here’s what you need to know about Medigap open enrollment and the best times to enroll, as well as opportunities to switch plans.

When is the Medicare Supplement open enrollment period?
Unlike most other Medicare coverage, there’s not a set time of the year for Medicare Supplement Insurance open enrollment. Each Medicare beneficiary has their own Medigap open enrollment period.

Your Medigap open enrollment period starts the first month you have Medicare Part B and are 65 or older, and it lasts for six months. After the period ends, it never happens again (but some states have their own rules that might offer you other opportunities).

During your six-month Medigap open enrollment period, companies can’t factor your health or medical history into pricing or coverage decisions
[1]
. That is, they can’t use medical underwriting to charge you more or deny your application because of your current health status or medical history.

Outside of your Medigap open enrollment period, insurance companies can charge you higher premiums or outright refuse to sell you a new plan due to your health or your medical history. As a result, switching plans after you first sign up can be difficult and expensive.

» MORE: Best Medicare Supplement Insurance companies

What are Medigap birthday rules?
In some states, laws or regulations give you additional opportunities to switch Medigap policies without medical underwriting under certain circumstances. These opportunities are often available for a certain number of days per year starting on your birthday, so they’re called “birthday rules.”

Birthday rules differ significantly between states in terms of time periods, restrictions and other details. You can find information on the rules that apply to you through your State Health Insurance Assistance Program, or SHIP. Visit shiphelp.org to find yours.

What is the Medicare Supplement free look period?
When you switch Medigap policies, you enter a 30-day “free look period”
[2]
. This period gives you time to decide whether you want to keep the new policy or go back to your old policy.

When you apply for a new Medigap policy, you’ll have to promise to cancel your existing policy as part of the application. To take advantage of the free look period, don’t cancel it right away. Wait until you’re sure you want to keep the new policy, as long as you decide within 30 days.

During the free look period, you need to pay the premiums for both policies.

What are Medigap guaranteed issue rights?
Switch Medigap plans when you lose existing coverage
In certain circumstances, you have a guaranteed issue right to buy certain Medicare Supplement Insurance policies without medical underwriting. For example, if your Medigap company goes bankrupt, breaks the rules or otherwise stops covering you through no fault of your own, you're guaranteed the right to buy another policy.

Switch to Medigap when you lose Medicare Advantage coverage
Guaranteed issue rights can also apply if you don’t already have Medicare Supplement Insurance. Here are some situations in which you have a guaranteed issue right to switch from Medicare Advantage to Original Medicare with a Medigap policy
[3]
:

Your Medicare Advantage plan is leaving Medicare.

Your Medicare Advantage plan stops covering your area.

You move out of your Medicare Advantage plan’s service area.

The Medicare Advantage plan has misled you or otherwise not followed the rules.

When you have a guaranteed issue right because of any of the circumstances above, you can buy Medigap Plans A, B, D, G, K or L, plus Plan C or Plan F if you qualify. (Medigap Plan M and Plan N aren’t included in the federal law that sets up guaranteed issue rights
[4]
.)

» MORE: Compare Medicare Supplement Insurance plans

What are Medigap trial rights?
You also have a trial right to go back to Original Medicare and a Medigap policy within a certain period after you try another kind of Medicare coverage, such as Medicare Advantage; the Program of All-Inclusive Care for the Elderly, or PACE; or a special kind of Medigap policy called Medicare Select. Like a guaranteed issue right, a trial right means that insurers can’t refuse to sell you a policy or charge you more because of your health or medical history.

Switch to Medigap after trying Medicare Advantage
If you had Medicare Advantage first
If you joined Medicare Advantage or PACE when you turned 65 and first became eligible for Medicare Part A, and then you decide to switch to Original Medicare within the first year, you can buy any Medigap policy offered by any insurer in your state. (You can buy Plan C or Plan F only if you qualify.)

If you had Medigap first
If you had a Medigap policy, dropped it to join a Medicare Advantage plan or try a Medicare Select policy, and then decide you want to switch back within the first year, here’s what you have the right to buy:

Is the same Medigap policy you had before still available from that insurer?

Yes

You can buy the same policy from that insurer.

No

You can buy Medigap Plans A, B, D, G, K or L, plus Plan C or Plan F if you qualify, from any insurer in your state.

Can I enroll in Medigap during Medicare or Medicare Advantage open enrollment?
Yes. If you have Original Medicare, you can apply for a Medicare Supplement Insurance policy at any time. If you have Medicare Advantage and you’re switching to Original Medicare during an open enrollment period, you can also apply for a Medigap policy to accompany your Part A and Part B coverage.

In either case, if you’re outside of your Medigap open enrollment period and don’t have guaranteed issue rights or trial rights, insurers can charge you more or deny coverage based on your health or medical history.

Here are the two periods during the year when you can switch from Medicare Advantage to Original Medicare with a Medigap plan
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:

Medicare open enrollment runs from Oct. 15 to Dec. 7 each year. During this period, you can switch from Medicare Advantage to Original Medicare or vice versa and join, switch or leave Medicare Advantage plans or Medicare prescription drug plans (Part D).

Medicare Advantage open enrollment runs from Jan. 1 to March 31 each year. This is a more limited open enrollment period that offers a chance to switch or drop a Medicare Advantage plan that isn’t working for you.

The parts of Medicare
Read more about the different parts of Medicare and what they cover.

Medicare Part A (hospital insurance).

Medicare Part B (medical insurance).

Medicare Part C (Medicare Advantage).

Medicare Part D (prescription drug plan).

Medicare Supplement Insurance (Medigap).

If you have additional questions about Medicare, visit Medicare.gov or call 800-MEDICARE (800-633-4227, TTY 877-486-2048).