Massachusetts does not use the lettered Medicare Supplement (Medigap) plans, like Plan G or Plan N, that are sold in most states. Here the plans are called Core, Supplement 1 and Supplement 1A. Supplement 1 is only available to people who were eligible for Medicare before January 1, 2020. People new to Medicare can choose between Core and Supplement 1A.

State rules also give Massachusetts residents an extra Medigap enrollment window every year, from February 1 to March 31, with coverage starting June 1.

What does every Massachusetts Medigap plan cover?

The Division of Insurance (DOI) 2026 plan comparison lists these basic benefits in all three plans:

• Part A hospital copayments for days 61 to 90 ($434 a day in 2026) and days 91 to 150 ($868 a day)
• 365 additional lifetime hospital days, paid in full
• Part B coinsurance, in most cases 20% of the approved amount
• The first 3 pints of blood under Parts A and B

How do Core, Supplement 1 and Supplement 1A differ?

Based on DOI's 2026 comparison:

• Core. The basic benefits above, plus 60 days per calendar year in a mental health hospital beyond Medicare's 190 lifetime days. Core does not pay the Part A deductible, skilled nursing facility coinsurance, the Part B deductible or foreign travel care.
• Supplement 1A. The basic benefits, plus the Part A deductible ($1,736 per benefit period in 2026), skilled nursing facility coinsurance for days 21 to 100 ($217 a day), foreign travel coverage for Medicare-covered services needed abroad, and 120 mental health hospital days per benefit period. It does not pay the Part B deductible.
• Supplement 1. Everything in Supplement 1A plus the Part B annual deductible ($283 in 2026). Only for people eligible for Medicare before January 1, 2020. DOI notes that moving from Supplement 1 to 1A may be subject to restrictions.

DOI publishes a yearly listing of every carrier's Core, Supplement 1 and Supplement 1A premiums, and rates must stay in effect for at least 12 months.

When can I enroll?

The state regulation, 211 CMR 71.10, sets these open enrollment periods:

• Part B open enrollment. The six months starting with the first month you are both 65 or older and enrolled in Medicare Part B.
• Initial eligibility. The six months starting with the first month you become initially eligible for coverage.
• Annual open enrollment. February 1 to March 31 every year, for coverage effective June 1 (or when Medicare first takes effect, if earlier). Issuers must send their members a notice about it by January 1.

The same regulation bars Medigap issuers from denying, conditioning or pricing a policy for an eligible person based on age, health status, claims history or medical condition, and says no Massachusetts Medigap policy may have a waiting period or a preexisting condition exclusion.

How does this fit with Medicare's fall enrollment?

Medicare's own Open Enrollment runs October 15 to December 7, with changes taking effect January 1, according to Medicare.gov. That is when you can join, switch or drop a Medicare Advantage plan or a Part D drug plan. People already in a Medicare Advantage plan also have a Medicare Advantage Open Enrollment Period from January 1 to March 31.

The Massachusetts Medigap window, February 1 to March 31, is separate and set by state rules. If you are thinking about moving between Medicare Advantage and Original Medicare with a Medigap plan, map out both calendars before you make a change, so you are not left with a gap.

What should I compare?

• Whether the Part A deductible and skilled nursing coinsurance matter to you, which separates Core from Supplement 1A
• Whether you travel outside the U.S.
• Premiums for the same plan across carriers, using DOI's annual listing
• Whether you also need a separate Part D drug plan
• Your doctors and hospitals, if you are weighing a Medicare Advantage plan instead

FAQ

Can I buy Medigap Plan G or Plan N in Massachusetts? No. Massachusetts uses its own standardized plans: Core, Supplement 1 and Supplement 1A.

Who can still buy Supplement 1? Only people who turned 65 or first became eligible for Medicare (by age, disability or end-stage renal disease) before January 1, 2020.

What is the Massachusetts Medigap annual open enrollment? February 1 to March 31 each year, with coverage effective June 1, under 211 CMR 71.10(5).

Does Supplement 1A pay the Part B deductible? No. In DOI's 2026 comparison, only Supplement 1 covers the $283 Part B deductible.

Where can I get free help comparing plans? Massachusetts' SHINE program offers free health insurance counseling to people eligible for Medicare and their caregivers.

Next step

A licensed local insurance agent can compare Core and Supplement 1A premiums across carriers, check whether a Part D plan is still needed, and help you time any change around the fall Medicare enrollment and the February 1 to March 31 Medigap window. SHINE counselors offer free, unbiased help too.

Sources: Massachusetts Division of Insurance: Medicare Supplement Plans Offered in Massachusetts, 2026 (PDF, updated 12/29/2025), 211 CMR 71.10, Medicare.gov: Joining a plan, Mass.gov: SHINE Program.