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Learn from strangers

The 7 Medicare mistakes strangers on the internet keep warning you about

Spend an evening in Medicare threads on Reddit or any retirement forum and a pattern emerges: the same handful of regrets, posted again and again by different people in different years. None are exotic. All are preventable, and most trace to one rule nobody mentioned in time. Here are the seven, each with what it costs and the rule that prevents it, plus a 20-minute self-audit at the end.

By the Medicare Decoder team · Updated July 30, 2026 · 6-minute read · Figures are official 2026 amounts

Key takeaways

  • The seven recurring regrets: premium-only shopping, the missed Medigap window, the COBRA myth, the HSA collision, trusting HR’s guess on the 20-employee rule, unread Annual Notices of Change, and unclaimed IRMAA relief.
  • The Part B late penalty is 10% per 12 months late, permanently; the Part D penalty is 1% of $38.99 per month missed, permanently.
  • COBRA and retiree coverage do not count as current employment and do not protect you from penalties.
  • Enrolling in any part of Medicare, including free Part A, ends HSA contribution eligibility.
  • Most of these mistakes are checkable in 20 minutes with the audit list at the bottom of this article.
Jump to 1. Premium-only shopping 2. The Medigap window 3. The COBRA myth 4. The HSA collision 5. The 20-employee guess 6. The unread envelope 7. Unclaimed IRMAA relief 20-minute self-audit FAQ

Mistake 1: shopping by premium alone

The confession: "I picked the $0 plan. Then my knee surgery needed prior authorization, my orthopedist wasn’t in network, and my copays hit four figures."

The $0-premium Advantage plan is the most-clicked and most-regretted purchase in Medicare. The premium is one number; the product is the network, the prior-authorization rules, the drug formulary, and the annual out-of-pocket maximum. A plan can be free every month and expensive the one year you actually need it, which is the year that matters.

The fix: compare total expected yearly cost for your doctors and your drug list. Check each doctor against the specific plan (not the insurer brand), run prescriptions through Medicare.gov’s plan finder, and read the out-of-pocket maximum as the real price of a bad year.

Mistake 2: letting the 6-month Medigap window close while deciding

The confession: "I figured I’d decide on a supplement later. Later, they wanted my health history and quoted me double."

This is the single most common "I wish someone had told me" post in the genre. For 6 months after your Part B starts, every Medigap insurer in your state must sell you any plan at standard rates, no health questions. It’s one-time and it does not repeat. People treat the window as the time to think about it; the window is the time to act on it, because in most states, deciding late means underwriting.

The fix: if Medigap is even a maybe, buy inside the window. You can always drop it later without penalty; you often can’t get it back on the same terms. The rule in Medicare.gov’s own words is here.

Mistake 3: believing COBRA buys you time

The confession: "I had 18 months of COBRA, so I waited. Then I learned about the penalty. Then I learned it’s permanent."

COBRA feels like employer coverage. For Medicare’s enrollment rules it isn’t: only coverage from active, current employment lets you delay Part B safely. On COBRA or retiree coverage, the penalty clock runs anyway: 10% added to your Part B premium for every 12 months late, for life, plus possible months with no primary coverage at all while you wait for a general enrollment window.

The fix: if you’re on COBRA at 65, enroll in Medicare on your normal schedule. COBRA can sometimes wrap around Medicare for a while, but it never substitutes for it.

Mistake 4: the HSA collision

The confession: "HR said Part A is free, so I signed up while still working. My accountant found the excess HSA contributions at tax time."

Enrolling in any part of Medicare, including premium-free Part A, ends your eligibility to contribute to a health savings account. Worse, claiming Social Security triggers automatic Part A enrollment, and late Part A enrollment can be backdated up to six months, which can retroactively invalidate contributions you already made.

The fix: decide the HSA question before touching any enrollment. If you’re working past 65 at a 20+ employer and want to keep contributing, the usual play is to delay all of Medicare and stop HSA contributions about six months before you eventually enroll.

Mistake 5: trusting "I think we’re big enough" from HR

The confession: "HR assured me I could delay. The company had 17 employees. Medicare was supposed to be primary, and my claims got clawed back."

The 20-employee line decides everything about delaying Part B. At 20 or more employees, employer coverage stays primary and you can delay penalty-free, with an 8-month Special Enrollment Period when the job ends. Under 20, Medicare becomes primary at 65 whether you enrolled or not, which means the employer plan can refuse to pay what Medicare "should have," against coverage you don’t have.

The fix: get two things from HR in writing: the employee count as Medicare defines it, and confirmation that your coverage counts as active employment. A one-paragraph email is fine. "I think so" is a bad basis for a lifelong premium.

Mistake 6: letting the plan auto-renew unread

The confession: "Same plan five years. This January my oncologist was out of network and my inhaler moved to a tier that costs triple."

Advantage and Part D plans change every January: networks, formularies, premiums, copays, out-of-pocket maximums. The changes arrive in September in a document called the Annual Notice of Change, and every winter the forums fill with people whose envelope stayed sealed.

The fix: a fifteen-minute September ritual. Open the notice, check three things (your doctors, your drugs, the out-of-pocket max), and if anything moved against you, re-shop during October 15 to December 7. Loyalty to an insurance plan is not a virtue the plan reciprocates.

Mistake 7: paying an income surcharge that no longer fits

The confession: "Retired at 65, income dropped by 80%, and Medicare kept billing me like my final working year. For two years. Nobody mentioned the form."

IRMAA surcharges are computed from your tax return from two years ago, so new retirees routinely get billed at peak-career rates. In 2026 the surcharged Part B premiums run from $284.10 up to $689.90 a month. Entirely legal, frequently wrong about your actual situation, and correctable.

The fix: form SSA-44 asks Social Security to use your current income after a life-changing event, and retirement qualifies. Two pages plus documentation. The savings are often thousands per year, per spouse.

The 20-minute self-audit

  1. Window check: when did (or does) your Part B start? If you’re inside 6 months and don’t own a Medigap decision yet, that’s this week’s task.
  2. Coverage-source check: is your non-Medicare coverage from active employment at a 20+ employer? If it’s COBRA, retiree coverage, or a small employer, verify your enrollment status today.
  3. HSA check: contributing? Confirm you’re not enrolled in any part of Medicare and not receiving Social Security.
  4. Fit check: pull your plan’s current network status for each doctor and run your drug list through the plan finder.
  5. IRMAA check: if your premium includes a surcharge and your income has dropped since the tax year it’s based on, file the form.
  6. Paper check: find last September’s Annual Notice of Change. If you can’t, note the date: the next one lands this September.

The meta-mistake behind all seven: one input. One broker, one neighbor, one glossy mailer. Every regret thread has it. Cross-check anything you’re told, including by us, against Medicare.gov, and make the call with more than one voice in the room.

Questions people also ask

Does COBRA count as coverage for delaying Medicare?
No. COBRA and retiree coverage do not count as coverage from current employment, so they don’t protect you from the Part B late enrollment penalty of 10% per 12 months late, permanently. Only active-employment coverage at an employer with 20 or more employees allows a safe delay.
Can I contribute to an HSA while on Medicare?
No. Enrolling in any part of Medicare, including premium-free Part A, ends HSA contribution eligibility, and Part A enrollment can be backdated up to six months. If you plan to keep contributing past 65, you generally need to delay all Medicare enrollment and stop contributions about six months before you do enroll.
What is the Annual Notice of Change?
The document your Medicare Advantage or Part D plan mails each September listing every change for the coming January: premiums, copays, networks, formularies, and out-of-pocket maximums. Reading it, then re-shopping between October 15 and December 7 if needed, prevents most January surprises.
What happens if my employer has fewer than 20 employees and I don’t enroll at 65?
Medicare becomes your primary payer at 65 regardless of enrollment, so your employer plan can deny the portion Medicare would have paid, leaving you exposed, and late-enrollment penalties can apply on top. At small employers, enroll on time.
How do I fix a Medicare income surcharge after retiring?
File form SSA-44 with the Social Security Administration, citing your life-changing event (retirement or work reduction qualify) with documentation, and request that your current income be used instead of the two-year-old tax return.

Sources for this article

Figures checked against these sources in July 2026. We update within weeks when CMS publishes new amounts.

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