Educational only. I am not an actuary, attorney, licensed insurer, or Medicare counselor. This article explains federal Medigap Open Enrollment rules as Medicare.gov and CMS describe them. State law can add rights. Confirm with your State Insurance Department and SHIP. Official information: Medicare.gov or 1-800-MEDICARE. Free counseling: shiphelp.org.
Start here
Treat the six-month Medigap Open Enrollment Period as a one-time federal right, not as another October open-enrollment season. If you want standardized Medicare Supplement Insurance (Medigap) without medical underwriting, apply during that window. After it ends, federal law generally lets insurers refuse to sell, or charge more based on health, unless you qualify for a separate guaranteed-issue right.
People hear “open enrollment,” assume it returns every fall, and discover too late that Medigap’s federal open enrollment is a different clock. That mix-up is expensive.
What Medigap covers
Medigap is extra insurance from a private company that helps pay your share of Original Medicare costs: deductibles, coinsurance, and copayments. Medicare.gov: you generally must have Part A and Part B before you can buy it. You cannot use Medigap to pay Medicare Advantage cost sharing, and you generally cannot buy Medigap while you are in an Advantage plan unless you are switching back to Original Medicare.
Policies are standardized by letter in most states (A, B, C, D, F, G, K, L, M, N). Same letter, same basic benefits; price is what varies by company. Massachusetts, Minnesota, and Wisconsin standardize differently. Plans C and F are closed to people newly eligible for Medicare on or after January 1, 2020; Medicare.gov and the Medigap booklet explain that rule. This article does not rank letters or carriers.
When the six-month window starts
Medicare.gov: the best time to buy is during your Medigap Open Enrollment Period. That is the 6-month period that starts the first day of the month you are 65 or older and signed up for Part B.
Two conditions must both be true: age 65 or older, and Part B enrollment. CMS’s older Medigap guidance (CMS Medigap letter on timing) tracks the same idea under section 1882(s) of the Social Security Act: the first six months in which the individual is both 65 or older and enrolled in Part B.
During that period, under federal law:
- An insurer that sells Medigap in your state cannot refuse to sell you any Medigap policy it offers.
- It cannot use medical underwriting to deny you because of pre-existing health problems.
- It cannot charge you more because of those problems.
Medicare.gov also notes you generally get coverage that starts right away, with a limited exception: the company may still impose a waiting period of up to six months for coverage related to a pre-existing condition treated or diagnosed in the six months before the policy starts, unless prior creditable coverage shortens or eliminates that wait. Original Medicare still covers Medicare-covered services during any such wait; you remain responsible for Medicare’s coinsurance or copayment until Medigap begins paying for that condition.
This window does not return every fall
Medicare.gov’s Medigap basics page is explicit: your Medigap Open Enrollment Period is a one-time enrollment. It does not repeat every year like the Medicare Open Enrollment Period (October 15 through December 7).
Annual Election Period lets you change Advantage and Part D plans. It does not recreate federal Medigap guaranteed issue for people who already used or missed their six-month window.
If you are still working at 65
Delaying Part B because of employer group coverage based on current employment also delays the Medigap clock. Medicare.gov: when employer coverage ends, you can sign up for Part B without a late enrollment penalty. Your one-time Medigap Open Enrollment Period starts once you sign up for Part B and lasts six months, even if you sign up for Part B while you still have employer coverage.
That creates a planning problem. Employer coverage often fills a role similar to Medigap, so you may not need a Medigap policy yet. But if you take Part B early while still working, the six-month Medigap window starts then and will not restart later. Coordinate Part B timing with Medigap intent. Ask the employer benefits office how the group plan works with Medicare, then confirm Part B enrollment timing with Social Security.
Under 65, disability, and ESRD
Federal law generally does not require insurers to sell Medigap to people under 65. Some states require or allow sales to people eligible for Medicare because of disability or End-Stage Renal Disease (ESRD). Medicare.gov: if you have ESRD or a disability, you may not be able to buy the Medigap policy you want, or any Medigap policy, until you turn 65. When you turn 65 and have Part B, the federal six-month open enrollment applies. Check your State Insurance Department for under-65 rights.
After the window: narrower guaranteed-issue rights
If you are outside Medigap Open Enrollment, Medicare.gov says there is no federal guarantee a company will sell you a policy. If you can buy one, it may cost more because of past or present health problems. State rules can be more protective.
Separate guaranteed-issue situations (sometimes called Medigap protections) require a company to sell certain policies, cover pre-existing conditions, and not charge more because of health. Common federal triggers include losing certain other coverage through no fault of your own, or leaving a Medicare Advantage plan in specific situations (plan leaving Medicare, moving out of the service area, or certain trial rights). Timing is tight: Medicare.gov often describes applying as early as 60 days before coverage ends and no more than 63 days after it ends. Keep letters, notices, and claim denials as proof. Call your State Insurance Department or 1-800-MEDICARE if you think a protection applies.
Switching from Advantage back to Original Medicare during fall Open Enrollment does not automatically recreate full open-enrollment rights to every letter. Some situations give rights to a limited set of letters (often A, B, C, D, F, G, K, or L, subject to eligibility rules for C and F). Read the Medicare.gov “when can I buy” tool for your exact path.
How to buy without getting sold
Medicare.gov’s how-to-buy steps are practical:
- Confirm you have Part A and Part B, or will when the policy starts.
- Compare standardized letters for benefits you need (Part B excess charges, skilled nursing coinsurance, foreign travel emergency, and so on).
- Get quotes from multiple companies for the same letter. Same benefits; different price.
- Apply during open enrollment or with proof of a guaranteed-issue right so medical answers cannot be used to deny you or raise the price under federal rules.
- Generally, coverage begins the first of the month after you apply unless you request another date. If you have no documents after 30 days, call the company; after 60 days, call your State Insurance Department.
Watch illegal practices: it is illegal to sell Medigap to someone the seller knows is in Advantage (unless switching back), and illegal to claim Medigap is part of the Medicare program.
What to remember
Medigap Open Enrollment at 65 (or later when you first take Part B at 65 or older) is six months of federal protection against underwriting and health-based pricing. It starts on the first day of the month you meet both age and Part B conditions. It does not return every October. If you work past 65, your Part B start date is also your Medigap open-enrollment start date. Miss the window and you rely on narrower guaranteed-issue rights, state law, or underwriting. Confirm dates on Medicare.gov, then buy the letter that matches your Original Medicare cost-sharing risk, not the letter a TV ad ranks.
Sources
- Medicare.gov, When can I buy a Medigap policy?
- Medicare.gov, Get Medigap Basics
- Medicare.gov, Get ready to buy (Medigap Open Enrollment)
- Medicare.gov, How do I buy a Medigap policy?
- CMS, Medigap Open Enrollment Period timing guidance (mdgp0203)