If you're turning 65 this year, you've probably been buried in mailers promising free dental, gym memberships, and grocery cards.
That flood of advertising is pushing one specific path: Medicare Advantage.
What those glossy envelopes rarely explain is that the other option, a Medicare Supplement plan, works in a completely different way, and picking wrong can leave you with bills that stretch for years.
Medicare Advantage replaces Original Medicare with a private network plan, often with a $0 monthly premium but copays, prior authorizations, and a capped out-of-pocket limit that can run past $8,000 in 2025.
A Supplement, also called Medigap, pays after Original Medicare and can wipe out most of your remaining costs, but you'll pay a monthly premium that often starts between $100 and $250 depending on your state, age, and plan letter.
Medigap plans are priced by age in most states, which means the premium climbs as you get older.
Advantage premiums can be $0, but the trade-off shows up when you actually need care: a hospital stay, a specialist, or an expensive drug that needs approval first.
For a generally healthy 65-year-old, Advantage can be the cheaper bet.
For someone managing a chronic condition or expecting surgery, the math often flips fast.
The deadline matters more than the marketing.
You get a one-time, six-month Medigap open enrollment window that starts the month you're 65 and enrolled in Part B.
During that window, insurance companies generally can't turn you down or charge you more because of your health history.
Miss it, and in most states you can be denied or charged a higher rate for a pre-existing condition.
That single rule is why advisors tell people to decide carefully the first time around.
Standalone Part D plans pair with Medigap.
Advantage plans usually bundle drugs in, but their formularies and pharmacy networks change every January.
A medication that cost $40 in December can jump to a few hundred dollars in January if it moves to a different tier.
Always check your specific prescriptions against the plan's current list before you commit.
If you already have an Advantage plan and want to switch to Medigap later, you may face medical underwriting in most states.
A handful of states, including New York and Connecticut, offer more flexibility, but the rules vary widely.
That's why a five-minute call to your State Health Insurance Assistance Program, a free counseling service, can be worth more than any mailer.
They'll walk through your doctors, your drugs, and your budget without a sales pitch.
A practical move: write down your three most expensive prescriptions, your preferred hospital, and your monthly budget before you compare anything.
Then price one Advantage plan and one Medigap plan side by side using the same list.
The gap in total yearly cost is usually bigger than people expect, and it's rarely the same answer for two neighbors.
The honest takeaway is that neither option is universally better.
Advantage wins on low upfront cost and extras; Medigap wins on predictability and fewer surprises.
The real mistake is choosing based on a grocery card or a TV ad instead of your own medical history and your ability to handle a surprise bill.
Final Thoughts
Spend an hour on this decision now, because switching later is the part that gets expensive.