Medicare Advantage vs. Original Medicare + Medigap: The Complete Guide

The most expensive healthcare decision most retirees make is not which drug plan to choose or which hospital to use. It is the decision made at age 65 between Medicare Advantage and Original Medicare with a Medigap supplement — a choice that is largely irreversible and whose financial consequences compound for decades.

Most people receive this decision's framing from insurance agents or TV commercials, both of which have strong financial incentives to recommend Medicare Advantage. This article presents the tradeoffs without a sales agenda, using current 2026 costs and coverage data.

The Three Paths

Every person who enrolls in Medicare faces the same foundational choice among three coverage structures. Path A — Original Medicare alone — is almost never the right answer and is covered here primarily to clarify what it lacks. Paths B and C represent the real decision.

Path A — Original Medicare (Parts A and B) only: You pay $206/month for Part B in 2026, plus an unlimited 20% coinsurance on all covered services, plus the Part A hospital deductible of $1,676 per admission. There is no annual out-of-pocket maximum. A prolonged hospitalization, cancer diagnosis, or major surgery can generate $20,000–$50,000 or more in personal cost in a single year. Roughly 87% of Medicare beneficiaries carry some form of supplemental coverage precisely because of this exposure.

Path B — Medicare Advantage (Part C): A private insurance company receives a government payment to deliver your Medicare benefits. You still pay the Part B premium ($206/month) plus any plan premium — many plans charge $0 additional — and receive care through the plan's network. The plan must cover everything Original Medicare covers and typically bundles Part D drug coverage. The in-network out-of-pocket maximum in 2026 is capped federally at $9,250; the combined in- and out-of-network cap is $13,900.

Path C — Original Medicare + Medigap + Part D: You keep Original Medicare and add a standardized Medigap supplement policy from a private insurer. Medigap pays most or all of the cost-sharing that Medicare doesn't — the 20% coinsurance, the hospital deductible, skilled nursing costs. Add a standalone Part D drug plan, and your total monthly cost is approximately $366–$446 at age 65 in 2026 (Part B $206 + Plan G ~$120–$200 + Part D ~$40). In exchange, you see any doctor who accepts Medicare — nationwide, without network restrictions or prior authorization.

The Real Difference: Prior Authorization and Network Restrictions

The cost comparison between Medicare Advantage and Original Medicare + Medigap gets significant attention. The operational differences receive far less — but for many retirees, they matter more.

Prior authorization means a Medicare Advantage plan must approve certain services before they are delivered. This applies to hospital admissions, imaging, specialist procedures, durable medical equipment, and — critically — post-acute care in skilled nursing facilities. The approval process takes time. It can be denied. When you are acutely ill, waiting days for plan approval for a necessary treatment is not a hypothetical inconvenience — it is a real clinical risk. Original Medicare does not require prior authorization for covered services.

Network restrictions mean that, outside of emergencies, Medicare Advantage enrollees must use in-network providers for covered services. The plan's network is determined by the insurer, can change annually, and may not include every specialist or hospital in your area. A retiree who splits time between two states, travels extensively, or seeks care at a specialized cancer center or academic medical center may find that the network does not accommodate their actual care needs.

Neither of these restrictions applies under Original Medicare + Medigap. Any doctor or hospital that accepts Medicare is available — anywhere in the United States, without referrals, without prior authorization, without calling to check network status first.

Medigap: Plan G, N, and F Explained

Medigap policies are federally standardized — every insurer offering Plan G must cover the same benefits. The premium varies between insurers for the same plan letter; the coverage does not. For this reason, once you identify the right plan letter, you should compare premiums across multiple insurers to find the lowest cost for identical coverage.

Plan G is the most popular choice for new Medicare enrollees in 2026. It covers the Part A hospital deductible ($1,676), all Part B coinsurance (the 20%), skilled nursing facility coinsurance, hospice coinsurance, and foreign travel emergency care up to $50,000. The only gap is the Part B deductible of $257 annually — which you pay once per year before Plan G kicks in. After that $257, virtually all Medicare cost-sharing is covered.

Plan N provides similar coverage at a lower monthly premium — approximately $80–$140 versus $120–$200 for Plan G at age 65 — in exchange for copayments of up to $20 per doctor visit and up to $50 per emergency room visit. Plan N also does not cover Part B excess charges (the amount a doctor can charge above the Medicare-approved rate if they do not accept assignment). For a healthy retiree who sees doctors infrequently and whose physicians accept Medicare assignment, Plan N's lower premium can produce meaningful savings.

Plan F is the most comprehensive Medigap plan — it covers everything Plan G covers plus the Part B deductible and Part B excess charges. However, Plan F has been closed to new enrollees since January 1, 2020. If you were eligible for Medicare before that date and enrolled in Plan F, you may keep it. If you are newly eligible for Medicare, Plan F is not available — and Plan G provides nearly identical coverage for a lower premium.

The Medical Underwriting Trap — Why This Decision Is Largely Irreversible

This is the most important fact in Medicare planning that most people learn too late.

When you first enroll in Medicare Part B, you have a 6-month Medigap Open Enrollment Period during which Medigap insurers cannot deny you coverage or charge higher premiums based on your health. This is called guaranteed-issue. You can purchase any Medigap plan from any insurer at the standard rate, regardless of pre-existing conditions. This window does not repeat.

After this window closes, in most states, Medigap insurers can ask health questions and deny coverage entirely based on pre-existing conditions. A diagnosis of cancer, heart disease, diabetes, kidney disease, or dementia — any of which might be exactly the condition prompting you to want Medigap — can make you permanently uninsurable for Medigap at any price in most states.

The practical consequence: a 65-year-old who enrolls in a $0-premium Medicare Advantage plan because it looks like a great deal, develops a serious illness at 70, and then wants to switch to Original Medicare + Medigap for broader access to specialists — may be unable to purchase Medigap because the insurers will decline based on their health history.

This transforms the Medicare Advantage vs. Medigap decision from a simple annual cost comparison into a decision about insuring against future uninsurability. Purchasing Medigap at 65, when guaranteed-issue rights are active and you are healthy, locks in coverage that cannot be taken away regardless of what health conditions develop afterward. The Medigap premium is partly paying for that guaranteed coverage — not just this year's cost-sharing protection.

Five states — Connecticut, Massachusetts, Maine, New York, and Washington — require continuous Medigap open enrollment regardless of health status. Residents of these states can purchase Medigap at any time without medical underwriting, which significantly changes the calculus. In all other states, timing is everything.

IRMAA: How Your Income Affects Medicare Premiums

Medicare Part B (and Part D) premiums are not the same for everyone. The Income-Related Monthly Adjustment Amount (IRMAA) adds surcharges to Part B premiums for higher-income beneficiaries, based on MAGI from two years prior.

In 2026, a retiree whose 2024 MAGI was $106,000 or below (individual) pays the standard $206/month. At $133,001–$167,000, the premium rises to $391/month. At $500,000+, it reaches $649.90/month. Part D carries separate IRMAA surcharges on top of plan premiums.

The two-year lookback makes IRMAA a planning variable, not just a tax. A large Roth conversion, business sale, capital gain, or RMD spike in 2026 can trigger elevated Medicare premiums in 2028. Retirees who are executing a multi-year Roth conversion strategy should model each conversion year against the IRMAA brackets to avoid inadvertently crossing a threshold that costs more in premiums than it saves in future taxes.

IRMAA also applies to Medicare Advantage enrollees — the premium surcharge applies to Part B regardless of which coverage path you choose.

How to Evaluate a Medicare Advantage Plan

If Medicare Advantage is the right path for your situation, plan quality varies significantly. These factors matter most:

Star rating: CMS rates MA plans on a 1–5 star scale based on quality metrics and member satisfaction. Plans rated 4 stars or higher are eligible for quality bonuses from CMS and generally offer better benefits. Avoid plans rated below 3.5 stars.

Prior authorization frequency: Some plans require prior authorization for a narrow set of high-cost services; others require it broadly. Review the plan's Evidence of Coverage document for the prior authorization list before enrolling. High prior auth frequency is the most common driver of member dissatisfaction and care delays.

Network completeness: Verify that your primary care physician, key specialists, and preferred hospitals are in the plan's network. Do this every year — networks change annually. A provider in-network in 2026 may not be in 2027.

Out-of-pocket maximum: The federal cap is $9,250 in-network in 2026 — but individual plans set lower maximums. A plan with a $3,500 OOP maximum provides significantly better catastrophic protection than one at the federal limit. Compare OOP maximums across plans, not just premiums.

Drug formulary: If you take regular medications, verify the plan's formulary covers them at a manageable tier before enrolling. Plan drug coverage varies substantially, and switching drugs to fit a formulary is not always clinically appropriate.

The Annual Enrollment Trap in Medicare Advantage

Medicare Advantage plans can change their benefits, premiums, networks, and prior authorization policies every year. A plan that was excellent in 2026 may drop your specialist from its network in 2027, raise its OOP maximum, or add new prior authorization requirements.

This annual variability is one of the structural disadvantages of Medicare Advantage versus Medigap. A Medigap policy is guaranteed renewable — the insurer cannot change your coverage, cancel your plan, or alter your benefits for any reason other than non-payment. The plan letter's covered benefits are set by federal regulation and do not change. The only thing that changes in Medigap is the annual premium, which rises with age and general healthcare inflation — but the coverage structure itself is stable.

Every fall (October 15 – December 7), Medicare Advantage enrollees should review the Annual Notice of Change document that plans are required to send. This document details every benefit, premium, network, and formulary change for the upcoming year. Failing to review it is how retirees end up surprised by higher costs or lost coverage in January.

What to Do First

If you are approaching Medicare eligibility, the sequence of decisions matters:

1. Determine your Part B enrollment date — the month you turn 65 (or when you lose qualifying employer coverage). Your 6-month Medigap guaranteed-issue window begins the day Part B coverage starts.
2. Decide on the coverage path before the window opens using the decision framework. The underwriting risk means this is not a decision to make casually or reverse easily later.
3. If choosing Medigap: Compare premiums for Plan G (or Plan N if copays are acceptable) across all insurers in your area using your state's SHIP program or Medicare.gov's plan finder. Rates for identical coverage can vary 30–50% between insurers.
4. If choosing Medicare Advantage: Research plans in your area by star rating, OOP maximum, and network — not by premium alone. Verify every key provider is in-network before enrolling.
5. Enroll in Part D regardless of path unless your MA plan includes drug coverage. Delaying Part D enrollment past your initial enrollment period triggers a permanent late enrollment penalty of 1% of the national base beneficiary premium per month delayed.

Important Notes

• Medicare Advantage plan benefits, premiums, and networks change every year — review your plan's Annual Notice of Change each fall before the October 15 enrollment deadline.
• Medigap premiums are not regulated in most states and can rise significantly with age. A Plan G premium of $150/month at 65 may be $300–$400/month at 80 — factor this trajectory into long-term retirement budget projections.
• Part D out-of-pocket drug costs are capped at $2,000 in 2026 (down from $3,300 in 2023, a SECURE 2.0-era IRA Inflation Reduction Act change).
• IRMAA appeals are available if a major life event (retirement, divorce, death of spouse) reduced your income after the base year. File Form SSA-44 with the Social Security Administration to request a reduction.
• This is education, not individualized insurance or medical advice. Medicare decisions are highly individual — your health status, geography, income, and existing care relationships all affect the optimal choice. Your State Health Insurance Assistance Program (SHIP) offers free, unbiased Medicare counseling.

In ModernRetire

The Medicare Planner under Health -> Medicare walks through the full decision:

1. Enter your age, ZIP code, income (for IRMAA projection), and key healthcare factors (chronic conditions, travel patterns, existing specialist relationships) — the planner generates a personalized recommendation across all three coverage paths.
2. The IRMAA calculator shows how large income events — Roth conversions, RMDs, capital gains — affect your Part B and Part D premiums two years forward, and flags which planned transactions would push you into a higher IRMAA bracket.
3. The Medigap premium comparison shows estimated Plan G and Plan N premiums in your ZIP code by age from 65 to 85, illustrating the long-term premium trajectory and break-even analysis versus Medicare Advantage.
4. The enrollment calendar tool tracks your Initial Enrollment Period, identifies your guaranteed-issue window for Medigap, and sends reminders before the Annual Enrollment Period each October.