Medigap (Medicare Supplement)
Medigap, or Medicare Supplement Insurance, is a private policy that pays the deductibles, coinsurance, and copays a beneficiary owes under Original Medicare. Plans are standardized by letter (A through N) so benefits are identical across insurers for a given letter. Medigap only works with Original Medicare, never with Medicare Advantage.
- What it does
- Pays Original Medicare cost sharing
- Standardization
- Lettered plans A–N, identical benefits per letter
- Works with
- Original Medicare only, never Medicare Advantage
- Crossover
- Often auto-forwards after Medicare pays
What is Medigap?
Medigap, formally Medicare Supplement Insurance, is a private policy that pays the cost sharing Original Medicare leaves to the beneficiary. Because Part B has no out-of-pocket maximum and Part A carries a large per-benefit-period deductible, a supplement protects patients from open-ended liability.
Critically, Medigap only works alongside Original Medicare. A patient enrolled in Medicare Advantage cannot use a Medigap policy, and selling one to an MA enrollee is generally prohibited.
How are Medigap plans standardized?
Medigap plans are standardized by letter, so a Plan G from one insurer covers exactly the same gaps as a Plan G from another; only price and service differ. This is unusual in insurance and makes verification straightforward once you know the plan letter.
| Common plan | Typical coverage |
|---|---|
| Plan G | Nearly all gaps except the Part B deductible |
| Plan N | Most gaps, with small office/ER copays |
| Plan F (legacy) | Fullest coverage, closed to newly eligible |
How does Medigap billing work for providers?
Example: a patient owes $283 toward the 2026 Part B deductible and 20 percent coinsurance on a $500 allowed office visit. Medicare pays its 80 percent, then crosses the remaining balance to the patient's Plan G Medigap carrier, which pays the coinsurance so the patient owes only the deductible portion.
Frequently asked questions
Medigap pays the out-of-pocket amounts Original Medicare leaves to the patient: the Part A hospital deductible and coinsurance, the Part B 20 percent coinsurance, and depending on the plan letter, the Part B deductible and excess charges. It does not add new benefits like drugs or dental; it fills gaps in Parts A and B.
No. Medigap only supplements Original Medicare. It cannot pay toward Medicare Advantage cost sharing, and it is generally illegal to sell a Medigap policy to someone enrolled in an MA plan. If a patient switches to Medicare Advantage, their Medigap policy serves no purpose and is usually dropped.
In most cases automatically. Medicare processes the claim, pays its share, then crosses the claim over to the Medigap insurer through the coordination-of-benefits crossover process, which pays its portion without a separate submission. Providers should confirm crossover is active for that Medigap carrier rather than assume it.
Sources & further reading
Reviewed by the ImmediCare Solutions RCM team
Certified billers and coders handling claims across 50+ specialties nationwide. This entry is reviewed against current payer policy and CMS rules. Last review: Jul 5, 2026.
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