The short answer
Choose Medigap if you want predictable costs, travel or live in two states, have a chronic or serious condition, want any Medicare-participating specialist without a referral or prior authorization, and can absorb a premium that rises with age. KFF puts the 2023 average Plan G premium at $164 a month, and a typical Plan G leaves you paying only the Part B deductible, $283 in 2026, before Medicare-covered services are effectively fully covered.
Choose Medicare Advantage if premium is the binding constraint, your doctors are in network, you value extras such as dental, vision, hearing and fitness benefits, and you are comfortable with prior authorization and a network. KFF reports that 75% of individual Medicare Advantage enrollees with drug coverage pay no premium beyond the Part B premium of $202.90 in 2026.
The asymmetry that decides most cases: you can join a Medicare Advantage plan at almost any annual enrollment period, but in most states you can only buy a Medigap policy without medical underwriting during your one-time six-month Medigap open enrollment period. Advantage is a door that stays open; Medigap is a door that closes.
How each one is built
Original Medicare plus Medigap plus Part D is three products. Medicare pays its share of Part A and Part B services, the Medigap policy pays most or all of what Medicare leaves behind, and a standalone Part D plan covers drugs. Any provider in the country that accepts Medicare accepts your coverage. There are no networks and no referrals.
Medicare Advantage is one product from a private insurer that replaces how your Part A and Part B benefits are delivered, usually bundles drug coverage, and adds supplemental benefits. It has a provider network and an annual out-of-pocket limit that Original Medicare lacks. KFF reports that 61% of individual enrollees are in HMOs and 38% in local PPOs for 2026.
Prior authorization is the structural difference people feel most. KFF found that 99% of Medicare Advantage enrollees are in plans requiring prior authorization for at least one service in 2026, including 97% for inpatient hospital stays and 95% for skilled nursing stays. Insurers denied about 8% of nearly 53 million requests in 2024. Original Medicare generally does not require it.
Out-of-pocket limits and cost sharing
Original Medicare alone has no annual out-of-pocket cap, which is the entire reason supplemental coverage exists. In 2026, CMS set the Part A inpatient hospital deductible at $1,736 per benefit period, coinsurance at $434 a day for days 61 through 90, and skilled nursing coinsurance at $217 a day for days 21 through 100. Part B leaves you paying 20% of most outpatient services with no ceiling.
Medicare Advantage plans must cap Part A and Part B cost sharing. For 2026, KFF reports the CMS maximum out-of-pocket limit is $9,250 in network and $13,900 combined in and out of network, with plans averaging $5,421 in network, $4,636 for HMOs and $6,592 for PPOs. Those caps exclude Part D drug spending, which has its own separate $2,100 cap in 2026.
| 2026 exposure | Original Medicare alone | Medigap Plan G | Medicare Advantage |
|---|---|---|---|
| Annual limit on Part A/B cost sharing | None | Effectively the $283 Part B deductible | $5,421 average in network, up to $9,250 |
| Hospital deductible per benefit period | $1,736 | Covered by the policy | Plan per-day copays instead |
| Part B coinsurance | 20%, uncapped | Covered by the policy | Copays and coinsurance up to the plan limit |
| Provider access | Any provider accepting Medicare | Any provider accepting Medicare | Network, referrals and prior authorization |
| Drug out-of-pocket cap | $2,100 with a Part D plan | $2,100 with a Part D plan | $2,100, separate from the medical limit |
HMO enrollees should read one line carefully. KFF notes that HMOs generally cover only in-network care, so enrollees are typically responsible for 100% of out-of-network costs and often have no out-of-network limit at all.
What each option costs monthly
Everyone pays the Part B premium, $202.90 a month in 2026 per CMS, with income-related surcharges beginning above $109,000 of individual income or $218,000 filing jointly. Beyond that, the paths diverge.
KFF's Medigap analysis puts the 2023 average premium across all policyholders at $217 a month, with Plan G averaging $164 and Plan F, closed to people who turned 65 on or after January 1, 2020, averaging $274. Average Plan G premiums ranged from about $140 in the District of Columbia to $236 in New York.
Age is the other driver, and it depends on the rating method. KFF describes three: community rating, the same premium regardless of age; issue-age rating, priced by your age at purchase and not raised because of aging; and attained-age rating, which rises every year as you get older. Attained-age policies look cheapest at 65 and are usually the most expensive by 80, so ask which method a quote uses.
| Monthly cost component (2026) | Medigap Plan G path | Medicare Advantage path |
|---|---|---|
| Part B premium | $202.90 | $202.90 |
| Supplement or plan premium | About $164 average for Plan G, per KFF 2023 data | $15 average supplemental premium; 75% of enrollees pay $0 |
| Part D premium | About $36 average for a standalone plan | Usually bundled, about $8 of the average premium |
| Typical monthly total | Roughly $400 | Roughly $205 to $220 |
Plan N is the middle path: similar to Plan G but with copays of up to $20 for some office visits and $50 for some emergency visits, and no coverage of Part B excess charges. It was about 10% of Medigap policies in KFF's data and typically prices below Plan G.
Total cost of care in a good year and a bad one
Compare the annual total, not the premium. The figures below use the 2026 Part B premium, KFF's average Plan G and Part D premiums, and KFF's average Medicare Advantage in-network out-of-pocket limit.
| Scenario | Medigap Plan G + Part D | Medicare Advantage (average plan) |
|---|---|---|
| Healthy year, routine care only | About $4,835 in premium plus the $283 Part B deductible | About $2,615 in premium plus modest copays |
| Moderate year: specialist visits, imaging, one outpatient procedure | About $5,118, essentially unchanged | About $4,000 to $5,000 with copays |
| Bad year: hospitalization, rehab, chemotherapy | About $5,118, still essentially unchanged | About $2,615 plus up to $5,421 average, or $9,250 at the CMS maximum |
| Bad year, out-of-network care | No change, any Medicare provider is covered | Up to $13,900 combined, or unlimited on an HMO |
Read that as a spread. Medigap costs roughly $2,200 more per year in premium and delivers near-total predictability. Medicare Advantage saves that premium and asks you to accept a variable of up to several thousand dollars in any year you get seriously ill. Over a 20-year retirement, most people will have several of those years. KFF also notes that traditional Medicare beneficiaries with a Medigap policy report fewer cost-related problems accessing care than comparable Advantage enrollees.
The six-month window and medical underwriting
Medicare.gov states that your Medigap open enrollment period lasts six months, beginning the first month you have Part B and are 65 or older. During those six months an insurer must sell you any Medigap policy it offers in your state, cannot refuse you and cannot charge more because of your health history.
Afterward, federal law offers no such guarantee. Medicare.gov is explicit: your options may be limited, the policy may cost more because of past or present health problems, and there is no federal requirement that any company sell you a policy at all. Conditions such as diabetes with complications, recent cancer treatment, heart failure or a pending surgery commonly lead to a decline.
State law is the exception. KFF found only four states, Connecticut, Massachusetts, Maine and New York, require continuous or annual guaranteed issue for all beneficiaries 65 and older in traditional Medicare, regardless of medical history. A handful of other states offer narrower protections such as birthday rules that let existing policyholders switch to an equal or lesser plan annually. Check your own state before assuming you can change your mind later.
- Use the window if you are unsure. Starting with Medigap and switching to Medicare Advantage later is almost always possible. The reverse frequently is not.
- Guaranteed issue rights exist but are narrow. Medicare.gov describes rights when you lose other coverage, and requires you to apply no earlier than 60 days before that coverage ends and no later than 63 days after.
- Medigap and Advantage cannot be combined. Medicare.gov notes it is illegal for anyone to sell you a Medigap policy while you are enrolled in a Medicare Advantage plan.
- Employer coverage does not pause the clock. Medicare.gov says the six-month window starts once you sign up for Part B, even if you still have employer coverage.
Switching later, and what it takes
Advantage to Advantage is straightforward: use the annual Medicare open enrollment period, October 15 to December 7, for a January 1 start, or the Medicare Advantage open enrollment period from January 1 to March 31 to make one change if you are already in an Advantage plan.
Advantage to Original Medicare plus Medigap is the hard direction. You can drop the Advantage plan during those same windows, but in most states the Medigap insurer may underwrite you and can decline you. Two limited protections help: a trial right if you joined an Advantage plan when first eligible at 65 and change your mind within 12 months, and guaranteed issue rights if your plan leaves your service area or you move out of it.
Medigap to Advantage is easy at any annual enrollment period, though you should not cancel the supplement until the new coverage is confirmed in force.
The 12-month trial right is the most useful escape hatch in Medicare and the least known. If you take Medicare Advantage at 65 and dislike it, act inside the first year while a Medigap insurer still must accept you. Confirm the exact terms with your state insurance department before you cancel anything.
A decision checklist
- List your doctors and check every network. One out-of-network oncologist or cardiologist should decide this on its own.
- Price your drugs, not just the premium. Enter your exact prescriptions into each plan finder. The 2026 Part D out-of-pocket cap of $2,100 applies either way, but formularies and tiers differ sharply.
- Count how many states you live in. Snowbirds and frequent travelers usually belong on Original Medicare plus Medigap.
- Ask which rating method a Medigap quote uses. An attained-age policy that looks cheap at 65 can outprice a community-rated one by 75.
- Stress test a bad year. Compare Medigap premium against the plan out-of-pocket limit, up to $9,250 in network for 2026, not against average spending.
- Check your state protections. Only Connecticut, Massachusetts, Maine and New York guarantee ongoing Medigap access, per KFF. Elsewhere, treat your six-month window as one-time.
Plan availability, Medigap premiums and underwriting rules vary by state and carrier, and plans change every year. Nothing here is a quoted rate or a guarantee of acceptance. Our enrollment timing guide covers the dates that open and close these options.
Sources & further reading
- KFF — Medicare Advantage in 2026: Premiums, Out-of-Pocket Limits, Supplemental Benefits and Prior Authorization
- KFF — Key Facts About Medigap Enrollment and Premiums for Medicare Beneficiaries
- KFF — Medigap Enrollment and Consumer Protections Vary Across States
- Medicare.gov — When can I buy a Medigap policy?
- CMS — 2026 Medicare Parts A & B Premiums and Deductibles fact sheet
- Medicare.gov — How much does Medicare drug coverage cost? (2026 Part D figures)