Retirement Retirement Planning

7 Things Almost Every Retiree Gets Wrong When Signing Up for Medicare

Medicare sign-up mistakes can cost retirees for life.

By Sara Albertelli , Edited by Laura Hohenstein

Updated May 28, 2026

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Medicare covers tens of millions of Americans, but signing up the right way is harder than most people expect. The rules around enrollment windows, qualifying coverage, and plan selection are specific.

The deadlines are firm, and the consequences for getting them wrong are built to last. Miss the wrong window by even a month or two, and you may face a premium increase every year for the rest of your life.

We've included the most common mistakes that are easy to make and expensive to undo. Knowing what they are before you turn 65 is the easiest way to avoid wasting money in retirement.

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Missing your enrollment period

You have a seven-month window to enroll in Medicare. The three months before your 65th birthday, your birthday month, and the three months after.

Miss that enrollment window, and your Part B premium rises 10% for every 12-month period you were eligible but went without coverage. This penalty lasts for life. Therefore, even a brief delay adds hundreds of dollars a year to a bill with no expiration date.

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Assuming COBRA counts as qualifying coverage

Many people leave a job and use the Consolidated Omnibus Budget Reconciliation Act (COBRA) or retiree health coverage to bridge the gap to Medicare, assuming that protects them from penalties. Unfortunately, it doesn't.

The only coverage that qualifies as a valid reason to delay Medicare enrollment is active employer-sponsored insurance through your own or a spouse's current job. COBRA and retiree health plans don't meet that standard, and using them instead leaves you exposed to the same lifetime surcharges.

Skipping Part D because you're not on any medication

Healthy retirees often pass on prescription drug coverage because they don't need it yet, and while that seems like a smart choice, it can actually be pretty expensive.

The late enrollment penalty adds 1% of the national base beneficiary premium for every month you go without creditable drug coverage. The national base beneficiary premium is $38.99 in 2026. The longer you wait, the higher your penalty climbs, and once you enroll, that surcharge follows you into every plan you join.

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Picking a plan based on monthly premiums

A lower monthly premium looks appealing, but it rarely reflects the full cost of a plan. Plans with smaller monthly payments often carry higher deductibles and steeper copays, as well as narrower provider networks.

The drug formulary also may not cover your medications. The real cost of any Medicare plan only becomes clear when you look at the out-of-pocket maximum and consider what you'd actually pay if you needed significant care in a given year.

Letting your plan auto-renew without a review

Medicare Advantage and Part D plans update their terms every year. Premiums and networks can change, and formularies get revised.

Insurers are required to send an annual notice of change each fall, and the open enrollment window runs from October 15 through December 7. Skipping that annual review is one of the easiest ways to end up locked into a plan that no longer fits your needs or your budget.

Overlooking the IRMAA surcharge

Higher earners pay more for Medicare, and many don't find out until the first bill arrives. In 2026, individuals with income above $109,000 and couples earning above $218,000 pay an additional surcharge on both Part B and Part D premiums.

This is the Income-Related Monthly Adjustment Amount (IRMAA). The surcharge is based on your tax return from two years prior, so a higher earning year today may take you by surprise two years from now, and raise your Medicare costs well into retirement.

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Missing the Medigap open enrollment window

Medigap policies cover what Original Medicare leaves behind: deductibles, co-pays, and co-insurance. The open enrollment window lasts six months, starting the month you turn 65 and enroll in Part B.

During that window, insurers must sell you a policy at standard rates, regardless of your health. After it closes, they may deny your application or charge significantly more based on your medical history, with no federal guarantee of another chance.

Bottom line

Medicare's rules are designed to be permanent. Penalties do not expire, missed enrollment windows do not reopen, and there is rarely a clean way to undo a decision made in the wrong enrollment period.

Retirees who navigate it best tend to treat Medicare like a deadline-driven project and start learning the rules well before their 65th birthday. While most of these issues aren't reversible, the additional IRMAA surcharge may be. If you have had a significant life event, such as a divorce or the death of a spouse, that has significantly reduced your income since that high-earning year, you can ask Social Security to appeal the surcharge.

To set yourself up for a stress-free retirement, it's worth understanding this appeals process before you assume a higher premium is fixed for life.

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