If your situation is simple — you're turning 65, you're retired, no unusual coverage — the Turning 65 walkthrough covers you. This page is for everyone else. It covers the details and situations that trip people up. Each one has links where you can learn more or get free help.
The Medigap "one-way door" (the big one)
Many people choose Medicare Advantage first. They think: "If I don't like it, I can switch to Original Medicare with Medigap later." Often, you can't — or it's very hard to do.
You have the right to buy any Medigap policy (a supplement to Original Medicare) without medical questions, but only during one special 6-month window at age 65 (and a few other situations). After that, in most states a Medigap company can ask medical questions and can deny you coverage or charge you more because of past health problems. So if you get sick while on a Medicare Advantage plan, you may not be able to get a Medigap supplement and switch back to Original Medicare.
Medicare Advantage: prior authorization & networks
By law, Medicare Advantage must cover the same benefits as Original Medicare — it can't offer less. But the way you get care works differently. Here's what to know:
- Prior authorization (pre-approval). Advantage plans often require you to get permission before getting a service. They review whether the service is medically necessary. This means a covered service can be delayed or even denied, even though it's supposed to be covered. Some government reports found that some of these denials were for care that should have been approved. You can appeal a denial, and many are overturned when you challenge them. See Your Rights and Appeals timelines. The government has made the rules stricter (see Policy & Rule Changes).
- Networks. Advantage plans limit you to certain doctors and hospitals in your area. This makes it harder to keep a specific doctor or get care while traveling. Some hospitals have stopped working with certain plans. Original Medicare has no network — any doctor that accepts Medicare will see you.
- Original Medicare now has some prior authorization too: The government is testing prior authorization for certain services in six states, starting in 2026. This test runs until 2031. It doesn't change what's covered.
This doesn't make Advantage "bad." Often it has lower costs, extra benefits, and a yearly spending cap that Original Medicare doesn't have. But the two plans work differently. This difference matters most if you have ongoing health issues. Choosing Coverage explains the full trade-off.
Health Savings Accounts (HSAs) and Part A
This surprises people who are still working. Once you sign up for any part of Medicare — including free Part A — you stop being able to add money to a Health Savings Account. (You can still spend what's already in it.)
Here's the trap: When you start getting Social Security after age 65, Medicare Part A goes back into effect up to 6 months earlier. If you added money to your HSA during those earlier months, you put in too much, and you'll owe a tax penalty. If you have an HSA and are working past age 65, plan to stop adding to it well before you sign up for Medicare or start Social Security. See Working Past 65.
Automatic vs. active enrollment
What you need to do depends on whether you get Social Security:
- Already getting Social Security (or Railroad Retirement) before age 65? You are automatically signed up for Parts A and B. But you can say "no" to Part B if you don't want it yet.
- Not yet getting Social Security (many people wait to get a bigger payment)? Then nothing happens automatically. You must sign yourself up for Medicare through Social Security during your enrollment window. Many people think it's automatic and miss the deadline. See Enrollment & Deadlines.
IRMAA: higher premiums for higher incomes
If your income is over certain amounts, you pay an extra charge (IRMAA) on top of your regular Part B and Part D premiums. Two things confuse people:
- It's based on your tax return from two years ago. So if your income changed recently, it may not show up yet.
- If your income dropped because of a major life event — like retirement, losing your job, divorce, or a spouse's death — you can ask Social Security to recalculate using Form SSA-44. You don't have to wait two years. Many people don't know you can do this.
The amounts and income limits change every year. Check the current figures on medicare.gov. See also Understanding Your Costs.
ESRD (kidney failure) and Medicare Advantage
Two facts that are often wrong:
- People with End-Stage Renal Disease (kidney failure) can now join Medicare Advantage. This rule changed in 2021. Before that, most could not.
- If you have employer insurance and develop ESRD, there's a 30-month period when your employer plan pays first. After 30 months, Medicare takes over as the main payer.
These rules are complex. Confirm your own situation with Medicare and a SHIP counselor. See Medicare Under 65.
Turning 65 while already on Medicare for a disability
If you got Medicare early because you're disabled, turning 65 is important. It opens new choices. Around your 65th birthday, you get a new enrollment window and a new chance to get Medigap without medical questions. This second window is important because people under 65 have limited Medigap choices that vary by state. Turning 65 is often your first real chance to buy a Medigap supplement. See Medicare Under 65 and Medigap.
Unmarried and living together
Some Medicare rules depend on being legally married to a spouse. For example, you can delay Part B without a penalty if a spouse is working and you have coverage from their large employer. If you're in a domestic partnership or not legally married, these spouse-based rules may not work the same way. This is true even if you're on your partner's health plan. Don't guess. Confirm with the employer's benefits office and Social Security before you rely on delaying Part B. See Working Past 65.
COBRA and retiree coverage aren't a reason to delay Part B
Remember this because it affects many people: COBRA and retiree coverage do not let you delay Part B without a penalty. Only coverage from a job you're still working still lets you delay. If you're using COBRA or retiree coverage, enroll in Part B on time anyway. See Retiring or Losing Coverage for details.