Medigap Supplement
A private insurance policy that pays some or all of the cost-sharing gaps in Original Medicare — deductibles, coinsurance, and copays — with standardized plan letters A through N.
Medigap (Medicare Supplement) policies are sold by private insurers but are standardized by CMS into lettered plans. Plan G is the most popular among new enrollees (available to those eligible after January 1, 2020): it covers the Part A deductible and all Part A and Part B coinsurance, leaving only the Part B annual deductible ($240 in 2024) as an out-of-pocket cost. Plan N is similar but adds small copays ($20 for office visits, $50 for ER visits not resulting in admission).
Monthly premiums for Plan G range from $90–$300/month depending on age, gender, tobacco use, and state of residence. Some states (Massachusetts, Minnesota, Wisconsin) use different standardized plan structures. Premiums rise every year as the beneficiary ages; by age 80, Plan G premiums commonly reach $200–$400/month.
Medigap policies do not include drug coverage (Part D must be purchased separately) and cannot be used with Medicare Advantage plans. Guaranteed issue rights — when an insurer must sell you any plan regardless of health — apply during the 6-month Medigap open enrollment window after Part B begins. Applying outside this window allows medical underwriting, which can result in denials or surcharges for pre-existing conditions.
Real-World Example
A 65-year-old nonsmoker in Florida enrolled in Plan G at $138/month; her total annual Medicare cost (Part B premium $174.70 + Plan G $138 + Part D $28 = $340.70/month × 12 = $4,088/year) effectively capped her medical expenses regardless of utilization.