Medigap or Medicare Advantage? The Choice Is Easier Once You Know It's a One-Way Door

The most honest post in the Medicare threads we studied came from a 60-year-old doing homework early: "I didn't expect Medicare to leave so many gaps... the more I dig, the more surprised I am." The gaps are real (Original Medicare alone has no out-of-pocket ceiling at all), and the two ways to fill them get sold very differently: Advantage plans with television ads and $0 premiums, Medigap with a monthly bill and no glamour. The comparison below is straightforward. The part that isn't obvious, and that decides more outcomes than any benefit chart, is the timing rule at the end.

What each one actually is

• Medicare Advantage (Part C): a private plan that replaces Original Medicare. It must cover what Medicare covers, usually bundles drug coverage, and often adds dental, vision, or gym benefits. In exchange: a provider network (HMO or PPO), referrals and prior authorizations, and cost sharing as you go, capped in-network at a plan-set maximum that can run as high as $9,250 for 2026.
• Medigap (Medicare Supplement): private insurance that rides alongside Original Medicare and pays the deductibles and 20% coinsurance Medicare leaves behind. Plans are standardized by letter (G and N are today's workhorses): any doctor in the country that takes Medicare, essentially no networks or prior auth, highly predictable costs. The price: a real premium every month (commonly $100 to $300 by age, plan, and state), and you add a separate Part D plan for drugs.

The honest comparison

• Money in a healthy year: Advantage wins. $0-premium plans exist nearly everywhere; Medigap's premium arrives whether or not you see a doctor.
• Money in a bad year: usually Medigap. A serious diagnosis under Advantage means cost sharing to the cap (up to $9,250 in-network in 2026, more if the plan has out-of-network exposure), plus the friction of authorizations mid-illness. Medigap G's bad year is roughly the Part B deductible plus premiums.
• Doctor freedom: Medigap, decisively. Any Medicare provider, any state, no referrals. Advantage networks are local, change yearly, and directory accuracy is its own problem. Snowbirds and people with out-of-state specialists feel this immediately.
• Friction: Medigap has almost none. Advantage brings prior authorization on imaging, procedures, and post-hospital care; KFF's data shows those denials get overturned more than 80% of the time when appealed, which tells you both that appeals work and that the denials happen.
• Extras: Advantage, sort of. Dental and vision benefits are real but often capped low; read the actual benefit, not the ad.
• Simplicity: a tie that surprises people. Advantage is one card and one plan; Medigap plus Part D is two premiums but almost zero decision-making at the point of care.

The one-way door: why timing beats analysis

Here's the rule that should headline every Medicare seminar. Your [Medigap open enrollment period](https://www.medicare.gov/health-drug-plans/medigap/ready-to-buy/when) runs 6 months from the month you're 65+ and enrolled in Part B. During it, insurers must sell you any policy they offer at standard rates, no health questions. After it, in most states, buying or switching to Medigap means medical underwriting: the insurer can decline you or price you up for the diabetes, heart condition, or cancer history you've acquired since. (A handful of states, including New York and Connecticut, require year-round guaranteed issue, and some others have annual birthday or anniversary rules; check yours.) The practical consequence: Advantage is easy to enter and, once your health turns, can be hard to leave for Medigap. Every fall's open enrollment lets you switch Advantage plans or return to Original Medicare, but Original Medicare with no supplement and no cap is exactly the exposure Medigap exists to fix.

How to actually decide (and it's allowed to be simple)

1. If you can afford the Medigap premium without strain, and you value doctor freedom or expect real healthcare use in the next decade, Medigap G or N plus a cheap Part D plan is the buy-once-cry-once choice, made safely only inside your 6-month window.
2. If the premium genuinely doesn't fit the budget, a well-chosen Advantage plan is a legitimate answer: check that your doctors and hospital are in-network, your drugs are on the formulary, and read the plan's maximum out-of-pocket as the real price tag.
3. If you're torn, use the trial year deliberately: try Advantage at 65, set a reminder for month 10, and make the permanent call with a year of experience while the Medigap door is still guaranteed open.
4. Get the free second opinion either way: your SHIP counselor (877-839-2675) compares actual plans in your ZIP code and sells nothing, and our Medicare appeals and enrollment-penalty guides cover the adjacent traps.