6 Common Medicare Mistakes to Avoid in2025-2026 (And How to Fix Them)

Medicare has more moving parts than most people expect, and the penalties for getting the timing wrong are permanent, not one-time fees. Here are the six mistakes we see most often, in plain English, along with exactly how to avoid or fix each one.

Mistake 1: Assuming COBRA or Retiree Coverage Delays Part B Without Penalty

This is the single most expensive misconception in Medicare enrollment. COBRA and retiree health plans are not considered active employer coverage, so they don’t protect you from the Part B late enrollment penalty. Only active coverage through a current employer with 20 or more employees qualifies. If you retire and elect COBRA instead of enrolling in Part B, the penalty clock starts the month your active coverage ends, not when COBRA runs out.

The fix: Get written confirmation from HR on whether your post-retirement coverage is active or COBRA/retiree. If it’s COBRA or retiree coverage, enroll in Part B during your 8-month Special Enrollment Period regardless.

Mistake 2: Missing the Initial Enrollment Period

Your Initial Enrollment Period (IEP) is a 7-month window: three months before your 65th birthday month, your birthday month, and three months after. Miss it without qualifying employer coverage, and you’ll face a lifetime 10% penalty on Part B for every 12-month period you delayed, plus a gap in coverage until the next General Enrollment Period.

The fix: Mark your calendar three months before your 65th birthday. If you’re unsure whether you qualify for an exception, verify it before your window closes, not after.

Mistake 3: Not Reading Your Annual Notice of Change

Every Medicare Advantage and Part D plan sends an Annual Notice of Change by September 30, outlining what’s changing for the next plan year: premiums, deductibles, copays, provider networks, and drug formularies. Skipping it means you could auto-renew into a plan that no longer covers your doctor or your prescriptions the way it used to.

The fix: Read it every year, even if you liked your plan last year. Compare it against other options during the Annual Enrollment Period, October 15 through December 7.

Mistake 4: Confusing Medicare Advantage and Medigap

These are fundamentally different products sold by private insurers, and mixing them up leads to real coverage surprises. Medicare Advantage replaces Original Medicare with a private plan, usually network-based, often with a $0 premium and extra benefits like dental and vision, but with an annual out-of-pocket cap and network restrictions. Medigap supplements Original Medicare, working with any provider that accepts Medicare nationwide, with no networks, but a higher monthly premium and no dental or vision built in.

The fix: Decide based on your actual priorities: lower monthly cost and extra benefits favor Medicare Advantage; provider flexibility and predictable costs favor Medigap. There isn’t a universally “better” option, only a better fit for your situation.

Mistake 5: Not Checking the Drug Formulary Before Enrolling

Every Part D and Medicare Advantage plan has its own formulary, the specific list of covered drugs and what tier they fall into. A plan that looks cheap on premium can end up expensive if your actual prescriptions land in a high-cost tier or aren’t covered at all.

The fix: Before enrolling, run your full medication list, including dosages, against each plan’s formulary. Under 2026 rules, all Part D plans cap your annual out-of-pocket drug costs at $2,100, but what you pay to reach that cap still depends heavily on your specific formulary tier placement.

Mistake 6: Not Realizing You May Qualify for Help Paying Your Costs

Medicare comes with real monthly costs, premiums, deductibles, copays, and many people assume assistance programs are only for those with much lower income than theirs. Medicare Savings Programs (QMB, SLMB, and QI) can pay your Part B premium or more if your income and assets fall under certain limits, and qualifying automatically enrolls you in Extra Help for prescription drug costs too.

The fix: Apply even if you’re not sure you’ll qualify. For 2026, a single person can often qualify for at least partial help with income up to roughly $1,816 a month, and some states use more generous limits. See our full Medicare Savings Programs guide for the exact 2026 numbers.

The Common Thread

Every mistake on this list comes down to the same root cause: assuming last year’s plan, or a temporary coverage bridge, will keep working the same way going forward without a fresh look. Medicare rewards people who check their assumptions annually and penalizes people who don’t, permanently in some cases. A once-a-year review costs you nothing and catches most of this before it becomes expensive.

A Simple Annual Checklist

Most of these mistakes share the same fix: a short review, once a year, before your enrollment window matters. Here’s what that looks like in practice.

Every September: Read your Annual Notice of Change in full before it lands in a pile of mail. Note anything that changed in premium, network, or formulary.
Every October 15 to December 7: Compare your current plan against at least two alternatives during AEP, even if you expect to stay put. Confidence in your choice is worth ten minutes of comparison.
Any time your income changes: Check whether a Medicare Savings Program or Extra Help now applies to you. Eligibility isn’t static, and a drop in income can open a door that wasn’t there last year.
Any time your employment status changes: Confirm in writing whether your coverage is active employer coverage, COBRA, or retiree coverage, and know your Special Enrollment Period deadline before you need it.
Any time a new prescription is added: Re-check your plan’s formulary. A single new medication can change which plan is actually cheapest for you.

Common Questions About Avoiding Medicare Mistakes

Which of these mistakes is the most expensive?

The Part B late enrollment penalty from mistake 1 or 2 is typically the costliest because it compounds for life. A five-year gap adds roughly $101 a month to your Part B premium permanently, which can total tens of thousands of dollars over a full retirement. Formulary mismatches and missed savings programs cost real money too, but they’re correctable year to year. A late-enrollment penalty generally isn’t.

I think I’ve already made one of these mistakes. What now?

Don’t guess at the fix on your own. Some of these, like a formulary mismatch, are correctable at your next enrollment window. Others, like a late enrollment penalty, have narrow relief options that depend on your specific history. A licensed agent or your local SHIP counselor can tell you which category you’re in and what, if anything, can still be done.

Do these mistakes apply the same way to Medicare Advantage and Original Medicare?

Some do, some don’t. The Part B enrollment penalty applies regardless of which path you choose, since it’s about Part B itself. The Annual Notice of Change and formulary mistakes apply directly to Medicare Advantage and Part D plans specifically. Medigap has its own separate timing rule, the six-month guaranteed-issue window after enrolling in Part B at 65, which carries its own version of “don’t miss the window.”

Take the free Medicare Clarity Score™, a 3-minute check that flags coverage gaps, penalty risk, and overpayment before you talk to anyone. Or call Scott Bowling directly at 512-844-3983. Texas License #2882146. No pressure. No jargon. Just clear answers.

Last updated: August 2026. We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov or 1-800-MEDICARE to get information on all of your options. We are not connected with or endorsed by the United States government or the federal Medicare program.