Medicare
Medicare’s most expensive mistakes usually aren’t about picking the wrong plan. They’re about missing a window — because some penalties last for life, and some choices can’t easily be undone.
The penalties that never go away
Miss your initial enrollment window for Part B or Part D without qualifying coverage elsewhere, and you can face late-enrollment penalties added to your premium for as long as you have Medicare. These aren’t one-time fees; they’re permanent surcharges that grow the longer you wait. If you’re still covered by an employer plan past 65, you may be fine to delay — but that’s a determination to make deliberately, not by default.
Your most protected moment: Medigap open enrollment
The six months starting with your Part B effective date are the single most protected window in all of Medicare. During Medigap open enrollment, insurers must sell you any Medigap plan at their best available rate — no medical underwriting, no denial for health history. Once that window closes, an insurer in most states can ask health questions, charge more, or turn you down entirely. If you think you’ll ever want Medigap’s any-doctor flexibility, this is the moment to act.
The Medicare Advantage trial period
Choosing Medicare Advantage at 65 isn’t irrevocable — at first. You get a 12-month trial period to switch back to Original Medicare with guaranteed Medigap rights, and the same protection applies the first time you switch from Medigap to Advantage. There’s also a 30-day “free look” when changing Medigap policies. After those windows, moving from Advantage to Medigap can mean underwriting — and for someone whose health has changed, that door may effectively be closed.
The window people forget: every fall
Networks, drug formularies, and premiums change every year. The retirees who quietly overpay are usually the ones who set a plan at 65 and never look again. Put the fall annual enrollment period on your calendar and re-shop your Part D or Advantage plan against what you actually take and who you actually see. Free, unbiased, state-specific help is available from your State Health Insurance Assistance Program (SHIP).
Key takeaways
- Part B and Part D late-enrollment penalties can raise your premiums for life.
- Your six-month Medigap open enrollment is the only guaranteed, no-underwriting chance to buy any plan.
- Advantage has a 12-month trial period — after that, switching to Medigap may require underwriting.
- Review coverage every fall; plans change even when your health doesn’t.
Sources
Enrollment periods, penalties, and trial-period rules summarized from Medicare.gov and educational materials on Medicare choices published by Vanguard (2026). Contact your state SHIP for free personalized help.