Medicare Supplement (Medigap) Plans & Underwriting

What it is

A Medicare Supplement, also called Medigap or a Med Supp, is a private policy that works alongside Original Medicare to help pay the "gaps" — the deductibles, copays, and coinsurance that Parts A and B leave to the beneficiary. It is not a stand-alone plan: you must have Medicare Parts A and B to buy one, and you cannot use a Medigap policy with a Medicare Advantage plan.

Medigap policies do not include prescription drugs — a separate Part D plan is needed for that. They also generally don't cover routine dental, vision, hearing, or custodial long-term care.

Standardized plans (lettered A–N)

Medigap plans are standardized by the federal government and identified by letters (A, B, C, D, F, G, K, L, M, N). Because they're standardized, a given letter covers the same benefits no matter which company sells it — the main difference between companies is price and service. (Massachusetts, Minnesota, and Wisconsin standardize their plans differently.)

What the lettered plans can cover (varies by letter):

• Part A coinsurance and hospital costs up to an extra 365 days after Medicare runs out
• Part B coinsurance or copayment
• Blood (first 3 pints)
• Part A hospice care coinsurance/copayment
• Skilled nursing facility care coinsurance
• Part A deductible
• Part B deductible *(only on older Plans C and F)*
• Part B excess charges *(only on Plans F and G)*
• Foreign travel emergency (up to plan limits)
• An annual out-of-pocket limit *(only on Plans K and L)*

The 2020 change (important)

For people who became eligible for Medicare on or after January 1, 2020, plans that pay the Part B deductible (Plans C and F) are no longer available. Newly eligible people instead choose from plans like D and G, which became the guaranteed-issue options for that group. Plans C and F (including High-Deductible F) remain available only to those who were eligible for Medicare before that date.

How the letters line up on coverage vs. premium

• Most coverage: Plans C, D, F, G (more benefits, higher premium)
• Middle of the road: Plans M and N
• Lower premiums / less coverage: Plans A, B, K, L

Plans K and L cover a percentage of certain benefits (K pays 50%, L pays 75% of some items) but include an annual out-of-pocket limit — once you hit it, the plan pays 100% of covered services for the rest of the year. High-Deductible Plan F and Plan G require you to pay covered costs up to an annual deductible first, then the plan pays 100%.

Part B "excess charges"

Only Plans F and G cover Part B excess charges — the extra amount a doctor who does not accept Medicare assignment is allowed to bill above the Medicare-approved rate. Some states don't permit excess charges at all, so this benefit matters more in states that do.

How Medigap premiums are set

All Medigap plans are guaranteed renewable — the policy can't be canceled as long as premiums are paid. Insurers price policies using one of three rating methods:

• Community-rated — everyone with the policy pays the same, regardless of age.
• Issue-age rated — your premium is based on your age when you bought the policy and doesn't rise just because you get older.
• Attained-age rated — your premium starts based on your current age and increases as you age (the most common method, though some states require community or issue-age rating).

With all three, premiums can still rise over time due to inflation and rising health-care costs. Other factors that affect premium include tobacco use, gender, ZIP code, when you enroll, household discounts, and payment method. Many carriers offer a household discount (often 7–20%) when two people in the same household are insured.

Underwriting: when health matters

Whether you have to answer health questions ("pass underwriting") depends on when you apply.

The Medigap Open Enrollment Period — your best window

Everyone aging in gets a six-month Medigap Open Enrollment Period (OEP) that starts the first month they have Part B and are 65 or older. During this window you have a guaranteed issue right: a company must sell you any plan it offers, cover pre-existing conditions, and cannot charge more based on your health. This is the ideal time to enroll. (Applying a bit early — often up to six months before — can lock in a rate.)

Guaranteed Issue (GI) rights outside the OEP

Outside the OEP, you may still get a guaranteed issue right (no underwriting) in certain situations defined by federal law, for example:

• Your Medicare Advantage plan leaves Medicare or your service area, or you move out of its area
• You're in the first year of an MA plan you joined when first eligible at 65 (a "trial right") and want to return to Original Medicare
• Employer/union/retiree/COBRA coverage that pays after Medicare is ending
• Your Medigap carrier goes bankrupt or your coverage ends through no fault of your own
• You were misled by a company or it broke the rules

Note: GI rights vary — some states add more rights than federal law (a few even offer annual or birthday-month windows). Always check your state.

When underwriting applies

If you want to buy or switch to a non-guaranteed-issue plan outside your OEP, you'll typically answer health questions about things like height/weight, recent hospitalizations, and diagnoses. The insurer uses your answers to decide whether to accept you, and at what rate.

• Most companies offer a preferred rate (non-tobacco users within height/weight ranges) and a standard rate (tobacco users or outside those ranges).
• Some conditions can lead to an immediate decline at some carriers; others offer higher-priced plans for less-healthy applicants.
• Underwriting typically takes about 7–10 days (anywhere from 1 to 30).

Practical takeaway for consumers: If a health condition could prevent you from passing underwriting later, it's important to choose, during your OEP, a plan you'll be comfortable keeping long-term — because switching later may require medical approval.

Who tends to be a good fit for Medigap

People often choose Medigap when they:

• Live in a rural area with limited MA networks
• Are on a fixed income and want predictable yearly costs
• Travel frequently (snowbirds) and want nationwide access to any Medicare provider
• Want to avoid networks, referrals, and surprise copays
• May save money filling prescriptions through Original Medicare + a stand-alone Part D plan
• Have or expect health issues and want the security of richer coverage while they can still get it

Medicare beneficiaries under 65

People under 65 on Medicare (due to disability or ESRD) may qualify for a Med Supp, but federal law doesn't require carriers to sell to them — it's left to each state. Availability and which plan letters are offered vary widely by state (Plan A is the most commonly available). Because of limited availability, an MA plan is sometimes the more practical option for under-65 beneficiaries.

See also: Medicare Basics — Parts A, B, C & D, Medicare Advantage vs. Medigap — Side by Side, Part D Prescription Drug Coverage, Medicare & ACA Enrollment Windows.