Every fall, millions of Americans on Medicare face the same fork in the road, and the wrong turn can quietly drain a retirement account.
The two main paths are Medicare Advantage (Part C) and Medicare Supplement plans, often called Medigap.
They behave nothing alike when the bills arrive.
Medicare Advantage is the all-in-one option.
Private insurers bundle your hospital, medical, and usually drug coverage into one plan, often with a $0 premium on top of the standard Part B charge.
The trade-off hides in the details: networks, referrals, prior authorizations, and copays that can stack up fast during a bad year.
A 2023 KFF analysis found that nearly half of eligible beneficiaries now choose Advantage, drawn in by extras like dental, vision, and gym memberships.
Medigap works on a completely different principle.
You keep original Medicare and buy a supplemental policy that covers most of what Medicare leaves behind, like the 20% coinsurance on many services.
You can see any provider in the country who accepts Medicare.
The catch is the price tag: monthly premiums commonly run $100 to $250 or more depending on your age, location, and plan letter.
The cost math flips depending on your health.
Someone who rarely sees a doctor may come out ahead on a low-premium Advantage plan.
Someone facing cancer treatment, a joint replacement, or a stretch in a skilled nursing facility can blow past thousands in Advantage copays that Medigap would have absorbed.
Consumer advocates repeatedly warn that the sickest enrollees feel the pinch hardest.
There's a timing trap that trips up a lot of people.
If you sign up for Medigap during your six-month Medigap Open Enrollment Period, which starts when you're 65 and enrolled in Part B, insurers generally can't reject you or charge more because of health history.
Miss that window and, in most states, you can be denied coverage or quoted a higher rate for a pre-existing condition.
Switching from Advantage back to Medigap later is where people get stuck.
Advantage plans usually include Part D, while Medigap does not, so you'd buy a standalone Part D policy separately.
That's an extra premium, but it also gives you flexibility to shop drug plans each year without touching your core coverage.
Advantage enrollees, by contrast, are locked into their plan's formulary and network pharmacies.
Pull your list of doctors and medications and check them against every plan you're considering.
Add up the worst-case out-of-pocket maximum, not just the premium, because that's your real exposure.
And check your state's Medigap rules, since a handful of states offer more generous switching rights than the federal baseline.
None of this is one-size-fits-all, and nobody can promise which path saves you money.
A licensed counselor through your State Health Insurance Assistance Program can walk you through your actual numbers for free, which beats guessing from a mailer.
The honest takeaway: Advantage plans win on upfront price, Medigap wins on predictability, and the gap between them widens exactly when you can least afford it.
Final Thoughts
Run your own worst-case scenario before you check a box, because reversing course later is far harder than choosing carefully now.