Missing enrollment important date costs you permanently

The biggest mistake is not enrolling when you first become may be able to access. Medicare has strict enrollment windows, and if you miss yours, you pay a penalty for life — not just once, but every month you have coverage. The penalty is 10% of the Part B premium for each year you were may be able to access but did not enroll, and it stacks.

Your initial enrollment window opens three months before the month you turn 65 and closes three months after. If you miss it and do not have employer coverage or another may have access to reason, you cannot enroll again until the next general enrollment period (January 1 to March 31), and the penalty applies retroactively. People who worked past 65 sometimes think they can enroll later without penalty — they cannot, unless their employer has 20 or more employees.

If you are already on Medicare and miss the important date to switch plans during annual enrollment (October 15 to December 7), you are locked into your current plan for the whole year. The only exception is if you have a may have access to life event like losing employer coverage or moving out of your plan's service area.

Key Takeaways

  • Missing your initial enrollment window at 65 triggers a lifetime penalty on Part B premiums, even if you enroll years later.
  • Failing to enroll in Part D (prescription drug coverage) when first may be able to access costs you 1% of the national base premium for each month you delay, added to your premium permanently.
  • Staying on Original Medicare without a Medigap or Medicare Advantage plan leaves you exposed to unpredictable out-of-pocket costs that can reach thousands per year.
  • Not reviewing your coverage annually during open enrollment means you may overpay for drugs or miss plans that better fit your doctors and medications.
  • Assuming all doctors and pharmacies accept your plan without checking first can result in surprise bills or having to switch providers mid-year.

Skipping Part D enrollment triggers a permanent penalty

Part D is prescription drug coverage, and it is separate from Part A and Part B. If you do not enroll in Part D when you first become may be able to access and you do not have other creditable drug coverage (like from an employer or union), you pay a penalty for as long as you have Medicare. The penalty is 1% of the national base beneficiary premium for each month you were may be able to access but did not enroll.

The national base premium changes every year, so the penalty amount changes too. In 2024, the base premium was around $34.70 per month, meaning a one-year delay costs roughly $4.16 extra per month forever. A five-year delay costs roughly $20.80 extra per month for life. This penalty is added to whatever plan premium you eventually choose.

The exception is if you have creditable coverage — meaning coverage as good as or better than Medicare's standard. Employer plans, TRICARE, the VA, and some state programs count. If you have creditable coverage, you can enroll in Part D later without penalty, but you must be able to prove it. Keep documentation from your employer or other source.

Choosing Original Medicare without supplemental coverage leaves you exposed

Original Medicare (Part A and Part B) covers a lot, but it does not cover everything. Part A has a deductible per hospital stay (currently $1,676 per benefit period), and Part B has a deductible and coinsurance. After you meet the deductible, you pay 20% of most services. There is no annual out-of-pocket maximum, which means your costs can grow without limit.

Many people choose Original Medicare and assume they are done. They are not. You have two options to fill the gaps: a Medigap policy (supplemental insurance) or a Medicare Advantage plan. Medigap policies are sold by private insurers and cover some or all of the costs Medicare does not — deductibles, coinsurance, and copays. Medicare Advantage is an alternative to Original Medicare run by private insurers; it usually has lower premiums but higher out-of-pocket costs and network restrictions.

If you enroll in Original Medicare without either, you could face a $3,000 to $5,000 hospital stay bill, or ongoing 20% coinsurance on doctor visits and tests. People often discover this too late — after they have already had a procedure and received a bill.

Not checking if your doctors and pharmacies are in-network

Medicare Advantage plans and some Medigap policies have networks. If you see a doctor or use a pharmacy outside the network, you pay more or the service is not covered at all. Many people enroll in a plan without confirming their current doctors are in-network, then discover mid-year that their primary care doctor is not covered.

Before you enroll in any plan, use the plan's provider search tool on Medicare.gov or the insurer's website. Search for your current doctors by name and specialty. Search for your pharmacy. If your doctor is not listed, call the plan directly — sometimes the directory is out of date. Ask whether your doctor is accepting new Medicare patients, because being in-network does not mean they are taking new patients.

If you discover after enrollment that your doctor is not in-network, you may have a short window to switch plans without penalty. This is called a special enrollment period, but it is not automatic — you have to request it and prove the change in circumstances.

Overlooking your medications when comparing plans

The cost of your drugs can vary wildly between plans. One plan might cover your blood pressure medication with a $5 copay, while another charges $50. Over a year, that difference is $540. Yet many people choose a plan based on premium alone and never look at the drug formulary — the list of covered medications and their costs.

Every Medicare Advantage and Part D plan has a formulary. Before you enroll, go to Medicare.gov's plan finder tool and enter your medications. The tool shows you the cost of each drug under each plan. Do this for every medication you take regularly, including inhalers, creams, and over-the-counter drugs your doctor recommends. Some plans cover certain drugs only if you try a cheaper version first (called step therapy), which can delay treatment.

Formularies change every year, so a drug that was cheap last year might be expensive this year. This is why reviewing your plan annually during open enrollment is critical. If your medications move to a higher cost tier, you may need to switch plans.

Forgetting to update your information after a life change

If you move, change your address, lose employer coverage, or get married, you must tell Medicare. Failing to update your information can result in missed notices, bills sent to the wrong address, or coverage gaps. Some life changes also give you a special enrollment period to switch plans outside the normal annual window.

Losing employer coverage is a common trigger. If you or your spouse retire and lose group health insurance, you have 63 days to enroll in a Medicare plan without penalty. If you miss this window, you pay the late enrollment penalty. Similarly, if you move out of your plan's service area, you can switch plans when ready.

Update your information through your Medicare account on Medicare.gov, by calling 1-800-MEDICARE, or by visiting your local Social Security office. Keep records of when you reported changes, in case there is a dispute later.

Paying full price for preventive services

Medicare covers many preventive services at no cost to you — no deductible, no coinsurance. This includes annual wellness visits, cancer screenings, cardiovascular screenings, diabetes screenings, and vaccinations. But you have to use an in-network provider and the service has to be ordered as preventive, not diagnostic.

The distinction matters. If your doctor orders a mammogram as a routine screening, it is free. If the mammogram finds something and your doctor orders a follow-up mammogram to investigate, that follow-up is considered diagnostic and you may owe coinsurance. Ask your doctor before the service whether it is being billed as preventive or diagnostic.

Many people do not know these services are free and pay out of pocket. Others know but do not schedule them because they assume there is a cost. Review the full list of covered preventive services on Medicare.gov and schedule the ones you are due for.

Assuming your Medigap or Medicare Advantage plan is the same every year

Plans change. Premiums go up, benefits shrink, networks change, and formularies shift. A plan that was perfect for you last year might be expensive or inadequate this year. If you do not review your options during annual enrollment, you could be overpaying or getting worse coverage than you need.

Set a calendar reminder for October 1, when the annual enrollment period opens. Spend an hour on Medicare.gov's plan finder tool. Enter your current medications, doctors, and pharmacy. Compare the plans available to you. Look at premiums, deductibles, out-of-pocket maximums, and drug costs. If you find a better plan, you can switch. The new coverage starts January 1.

If you are on a Medigap policy, check whether your premium is competitive. Medigap premiums vary by insurer, and shopping around can save hundreds per year. You have may provide issue rights (the right to buy without medical underwriting) only during certain windows, so timing matters.

Not understanding what "creditable coverage" means

Creditable coverage is health insurance that is as good as or better than Medicare's standard coverage. If you have creditable coverage when you become may be able to access for Medicare, you can delay enrolling in Part D without penalty. But you must be able to prove it.

Employer plans, TRICARE, the VA, and some state Medicaid programs count as creditable. Individual health insurance policies do not always count — it depends on the plan. If you are unsure, ask your employer's benefits department or your insurance company directly whether your coverage is creditable for Medicare purposes. Get the answer in writing.

If you delay Part D and later find out your coverage was not creditable, you owe the penalty retroactively. The penalty is calculated from the month you became may be able to access, not from the month you enroll. This can add up quickly.

Frequently Asked Questions

What happens if I miss my initial enrollment window at 65?

You can still enroll, but you pay a permanent penalty on Part B premiums (10% for each year you were may be able to access but did not enroll). You can enroll during the general enrollment period (January 1 to March 31), but the penalty applies retroactively. The only exception is if you had employer coverage or another may have access to reason to delay.

Can I switch Medicare plans anytime, or only during open enrollment?

You can switch during the annual enrollment period (October 15 to December 7). Outside this window, you need a may have access to life event — losing employer coverage, moving, getting married, or losing Medicaid. These events trigger a special enrollment period, usually 60 days long. Contact your plan or Medicare to confirm you may have access to.

How do I know if my doctor accepts Medicare?

Use the provider search tool on Medicare.gov or your plan's website. Search by name and specialty. If your doctor is listed, call their office to confirm they are accepting new Medicare patients. Directories are sometimes out of date, so a phone call is the safest check.

What is the difference between a Medigap policy and Medicare Advantage?

Medigap is supplemental insurance that works alongside Original Medicare and covers gaps like deductibles and coinsurance. Medicare Advantage is an alternative to Original Medicare run by private insurers; it usually has lower premiums but higher out-of-pocket costs and network restrictions. Both require separate Part D enrollment for prescription drugs, except some Medicare Advantage plans include drug coverage.

Do I have to pay for preventive services like cancer screenings?

No. Medicare covers many preventive services at no cost if they are ordered as preventive (not diagnostic) and performed by an in-network provider. This includes annual wellness visits, cancer screenings, and vaccinations. Ask your doctor before the service whether it is being billed as preventive to avoid surprise costs.