A 65-year-old picks a zero-premium Medicare Advantage plan during her Initial Enrollment Period. Three years later, after a diabetes diagnosis and a heart stent, she decides she wants the freedom of Original Medicare with a Medigap supplement. She can leave Medicare Advantage during the right enrollment period, but the Medigap insurer runs medical underwriting and turns her down. The plan she thought was a starting point became much harder to unwind.
The decision matters most for people approaching 65, already inside their first six months on Part B, or considering Medicare Advantage during the first year when limited trial rights may still apply. Someone already on Original Medicare with a Medigap policy has usually avoided the biggest version of this trap, but switching Medigap policies later can still involve state-specific rules and underwriting.
The one-way door most enrollees do not see
Federal law gives you a single six-month Medigap open enrollment window that starts the first month you are 65 or older and enrolled in Part B. Inside that window, insurers cannot deny you a Medigap policy because of pre-existing health problems. Outside that window, in most states, insurers can medically underwrite you, charge more because of health history, or refuse to sell you a policy at all.
Switching from Medicare Advantage back to Original Medicare can be straightforward during an allowed enrollment period. Getting the Medigap policy that makes Original Medicare financially predictable is the hard part. After the first-year trial right and the initial Medigap open enrollment window are gone, most states allow insurers to ask health questions and use the answers. The choice at 65 feels fully reversible. In many states, it is only partly reversible once the protected Medigap windows close.
What the numbers look like in a good year
The 2026 baseline numbers are straightforward. The standard Part B premium is $202.90 per month, and the Part B deductible is $283. The Part A hospital deductible is $1,736 per benefit period, and skilled nursing facility coinsurance is $217 per day for days 21 through 100. Medicare Advantage plans must cap in-network out-of-pocket spending at $9,250, with a combined in- and out-of-network ceiling of $13,900 for plans that cover out-of-network care. Those caps apply to Part A and Part B services, not Part D drug spending.
In a healthy year at age 66, the Advantage enrollee pays the Part B premium and may owe little else for medical care. The Original Medicare enrollee pays Part B plus a Medigap premium, and Plan G generally covers Medicare-approved cost-sharing after the Part B deductible. Advantage can win the healthy-year math, but the dollar spread depends on local Medigap premiums, drug coverage, and the Advantage plan’s cost-sharing.
The bad year trade-off
In a bad year at age 68 with a cancer diagnosis, out-of-network specialists, and infusion therapy, the Advantage enrollee could hit the in-network medical cap, face a higher combined limit on a PPO, or have nonemergency out-of-network care uncovered on an HMO. Part D drug costs are separate. The Plan G enrollee generally pays the Part B deductible and Medigap premium for Medicare-covered services. In a serious-care year, Plan G can erase several years of healthy-year premium savings.
The state exceptions worth checking
Federal rules are the floor. Connecticut and New York require continuous guaranteed issue for Medigap, Massachusetts has an annual guaranteed-issue period and broad market practice, and Maine requires at least an annual guaranteed-issue opportunity for Plan A. Other states, including California and Oregon, have limited anniversary or birthday-style switching rules, often restricted to equal or lesser benefits. In most states, the federal six-month window is still the main protection.
What to do
- If you are within six months of your Part B start date and undecided, price Medigap Plan G and Plan N while the federal open enrollment protection still applies. You can compare that premium against Medicare Advantage before the window closes, but buying Medigap later may be harder if your health changes.
-
If you are leaning Advantage anyway, look up your state’s Medigap rules before you enroll. In Connecticut, New York, Massachusetts, or Maine, the switch-back door may stay more open. In most other states, it narrows sharply after the initial federal window and any first-year trial right.
- Before each fall enrollment period, re-read your Advantage plan’s network directory, drug formulary, out-of-pocket maximum, and prior authorization rules, not just the premium. A zero-premium plan can still become expensive if the doctors, hospitals, drugs, or approvals you need are not handled favorably.
The First Medicare Choice Can Shape the Next Decade
Medicare Advantage can be the right choice for a healthy new retiree who understands the network, cost-sharing, and state Medigap rules. The mistake is assuming the decision can always be reversed later under the same terms. Before the six-month Medigap window closes, treat the choice as a long-term access decision, not just a premium comparison.
Figures reflect the 2026 plan year. Premiums, deductibles, and coinsurance come from the CMS “2026 Medicare Parts A & B Premiums and Deductibles” fact sheet. Medicare Advantage out-of-pocket maximums come from KFF’s 2026 Medicare Advantage analysis. Medigap open enrollment, trial rights, plan benefits, and cost variation come from Medicare.gov. State Medigap consumer-protection details come from KFF and MedicareResources.
Contact [email protected] for any questions or corrections.
Top Gaining Stocks
Top Losing Stocks