Medigap (Medicare Supplement), explained

Medigap is private insurance you buy to pay your share of costs under Original Medicare, the copayments, coinsurance, and deductibles that Parts A and B leave behind. It works alongside Original Medicare; it does not replace it. To buy a policy you generally need both Part A and Part B.

The key thing that makes Medigap easy to shop: the plans are standardized. In most states there are ten plan types, named by letter (A, B, C, D, F, G, K, L, M, N). Every Plan G is the same Plan G no matter who sells it, the core benefits are set by law. What changes between companies is the price and the service, not the coverage.

Every Medigap plan helps with a shared core of costs, then the higher letters add more on top. Nearly all plans cover:

• Part A coinsurance and hospital costs, plus an extra 365 days after your Medicare benefits run out
• Part B coinsurance or copayment
• Part A hospice coinsurance or copayment
• The first three pints of blood for a procedure

Depending on the letter, a plan may also cover the Part A deductible, skilled nursing facility coinsurance, Part B excess charges, and foreign-travel emergency care. The one cost no newer plan can cover for you is the annual Part B deductible ($283 in 2026).

Of the ten letters, a handful account for the large majority of new purchases. Here are the five that matter most.

Plan G is the most common choice for people new to Medicare. It covers nearly everything Original Medicare doesn’t, the only gap you pay is the annual Part B deductible. After that, your covered costs are essentially zero. If you see doctors often or want the most predictable bills, this is the one to compare first.

Plan N trades a lower premium for a little cost-sharing: small copays at some office visits (up to $20) and the emergency room (up to $50), and it doesn’t cover Part B excess charges. Popular with healthy people who don’t mind paying a bit at the time of service.

Plan F is the most complete plan ever offered, it leaves you with virtually no out-of-pocket costs, but it is only available if you became eligible for Medicare before January 1, 2020. Newer enrollees can’t buy F or C. For those who qualify, it carries the highest premium.

High-deductible Plan G gives you the same coverage as regular Plan G but with a much lower premium in exchange for a high annual deductible. Good if you want comprehensive protection but prefer to pay less monthly and can absorb more upfront in a bad year.

Plan K pays a percentage (rather than all) of several costs in exchange for the lowest premiums, with an annual out-of-pocket limit after which it pays 100% for the rest of the year.

Because benefits are identical within a letter, price is where companies compete, and how they price matters as much as the starting number. There are three pricing methods:

• Community-rated: everyone pays the same premium regardless of age. It won’t rise just because you get older.
• Issue-age-rated: your premium is locked to your age when you buy. Buy younger, pay less, and it won’t climb with age.
• Attained-age-rated: starts cheapest but rises as you age. The lowest quote today can become the most expensive over time.

This is the trap in shopping on the first-year price alone. Two Plan G policies with the same benefits can diverge by hundreds of dollars a year a decade later purely because of pricing method. Ask which method a quote uses before you compare.

The best time to buy is your Medigap Open Enrollment Period: the six months that begin the month you’re 65 and enrolled in Part B. During this window an insurer must sell you any plan it offers at its best rate and cannot turn you down or charge more for health conditions, this is called guaranteed issue.

Miss it, and in most states the insurer can medically underwrite you: review your health, charge more, or decline you. That single window is the most valuable consumer protection in Medigap, which is why timing the purchase matters as much as choosing the letter.