Entering the Medicare system can feel like stepping into an alphabet soup of plans, deductibles, and timelines. One of the most critical decisions you will make is how to handle the costs that Original Medicare (Part A and Part B) leaves behind.
Original Medicare has no annual out-of-pocket limit. If you experience a serious medical event, the 20% coinsurance under Part B can quickly become financially devastating. That is where Medicare Supplement Insurance—commonly known as Medigap—comes into play.
This guide breaks down exactly how these plans work, why timing your enrollment perfectly is everything, and why two specific plans have cornered the market.
1. How Standardized Medigap Plans Work
Medigap policies are sold by private insurance companies, but they are tightly regulated and standardized by the federal government.
In most states, plans are labeled with letters (Plan A through Plan N). Because they are standardized, every plan with the same letter offers identical coverage, regardless of the insurance company selling it or the state you live in.
The Golden Rule of Medigap: A Plan G from Carrier X has the exact same medical benefits as a Plan G from Carrier Y. The only differences are the monthly premium, customer service, and the company’s history of rate increases.
Note: If you live in Massachusetts, Minnesota, or Wisconsin, your states use their own standardization systems rather than the lettered plans.
2. The Six-Month Guaranteed-Issue Window: Your One Shot
The single most critical concept to understand about Medigap is the Medigap Open Enrollment Period. This is a one-time, six-month window that triggers automatically the month you are both age 65 or older AND enrolled in Medicare Part B.
During this six-month window, you have what is called Guaranteed-Issue Rights.
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No Medical Underwriting: Insurance companies are legally required to sell you any Medigap plan they offer. They cannot look at your medical history, check your prescriptions, or ask about pre-existing conditions.
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No Premium Penalties: They must charge you the preferred (lowest) rate, regardless of your health status.
What happens if you miss this window?
Unlike the standard annual Medicare enrollment periods that happen every fall, the Medigap open enrollment window does not repeat.
If you try to buy a Medigap policy after these six months have passed, companies in most states are allowed to use medical underwriting. They can review your medical records, charge you significantly higher premiums, or deny you coverage entirely based on your health history. This means if you start with a different type of coverage (like Medicare Advantage) and want to switch to Medigap years later, a pre-existing condition could lock you out forever.
3. Why Plans G and N Have Become the Default Choice
If you are newly entering Medicare, you will quickly notice that the conversation almost exclusively revolves around Plan G and Plan N.
Historically, Plan F was the default choice because it covered 100% of all gaps, leaving the policyholder with zero out-of-pocket costs. However, federal law changed; anyone first becoming eligible for Medicare on or after January 1, 2020, can no longer purchase Plan F. This naturally pushed Plans G and N to the top.
Neither Plan G nor Plan N covers the annual Medicare Part B deductible ($283). You must pay that amount out-of-pocket first before the supplement kicks in. Once that deductible is met, here is how the two plans handle the rest:
Plan G: The “Set It and Forget It” Gold Standard
Plan G is the most comprehensive plan available to new enrollees.
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The Coverage: After you pay the Part B deductible, Plan G covers 100% of your remaining Medicare-approved costs. Hospital stays, surgeries, doctor visits, and physical therapy are all fully covered.
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Excess Charges: It also covers Medicare Part B Excess Charges. An excess charge occurs if a doctor does not accept “Medicare assignment” and bills up to 15% above the Medicare-approved rate. Plan G absorbs this completely.
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Best For: Those who want 100% predictability, see specialists frequently, and never want to look at a medical bill.
Plan N: The Cost-Saving Copay Model
Plan N offers very similar core protection to Plan G but introduces minor cost-sharing in exchange for lower monthly premiums.
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The Coverage: It covers the major gaps (like Part A hospital costs), but you are responsible for small copays: up to $20 per doctor’s office visit and up to $50 per emergency room visit (waived if you are admitted as an inpatient).
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Excess Charges: Plan N does not cover Part B excess charges. While rare (as 95%+ of providers accept Medicare assignment), you could owe a bit more if you see a doctor who charges excess fees.
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Best For: Healthy individuals who do not mind paying small copays at the doctor’s office in exchange for saving roughly $25 to $45 a month on their premium.