Medicare Part B Is Where Surprise Bills Start—Even If You’re Doing Everything Right

Key Takeaways

• Medicare Part B often triggers unexpected medical bills—even if you enroll on time and choose coverage carefully.

• Understanding how premiums, coinsurance, and excess charges work in 2025 can help you avoid large, unplanned expenses.

Medicare Part B: What You Think You’re Getting

Medicare Part B is often seen as the heart of your healthcare coverage. It helps pay for medically necessary services like doctor visits, outpatient care, lab tests, preventive screenings, durable medical equipment, and more. If you’re enrolled in Original Medicare, Part B is essential.

But even if you’ve planned everything by the book—enrolled during your Initial Enrollment Period, paid premiums on time, and chosen what you believe is sufficient coverage—you could still end up facing surprise medical bills.

In 2025, the standard monthly premium for Part B is $185, and the annual deductible is $257. While that may seem manageable, the hidden costs begin to surface once you use the coverage.

Where the Surprise Charges Begin

Once you meet the annual deductible, Medicare Part B typically covers 80% of approved services. That leaves you responsible for the remaining 20% as coinsurance. The misconception is assuming that 20% will always be affordable. It isn’t—especially for high-cost outpatient services, expensive equipment, or specialist visits.

And that’s just the beginning.

Medicare Assignment: A Crucial Concept

Doctors and providers fall into three categories when it comes to billing under Medicare:

• Accept Medicare Assignment: These providers agree to accept the Medicare-approved amount as full payment.

• Do Not Accept Assignment: These providers can charge up to 15% more than the Medicare-approved amount.

• Opt Out of Medicare Entirely: These providers charge their own rates, and Medicare does not reimburse you.

In 2025, if you unknowingly see a doctor who doesn’t accept assignment, you could be responsible for “excess charges” up to 15% of the Medicare-approved amount, in addition to your 20% coinsurance.

Why Even Careful Planning Can Lead to Bills

You may have:

• Enrolled in Part B on time to avoid late penalties

• Picked your providers based on network information

• Scheduled preventive care covered under Medicare

And yet, you may still receive a bill because:

• The provider billed under a non-covered service code

• The procedure included a portion not covered by Medicare

• The provider doesn’t accept assignment

• You needed follow-up care outside your plan’s cost-sharing structure

Gaps That Medicare Part B Doesn’t Fill

Medicare Part B does not cover every medical cost. Here are some categories where you may face unexpected expenses:

• Prescription Drugs: Part B only covers drugs administered in a clinical setting. Retail pharmacy prescriptions fall under Part D.

• Dental, Vision, and Hearing: Routine exams, cleanings, glasses, and hearing aids are not covered.

• Long-Term Care: Custodial care in a nursing facility or at home is not paid for by Part B.

• Overseas Emergencies: Medicare generally doesn’t pay for care outside the U.S.

These gaps leave you exposed to out-of-pocket costs unless you have additional coverage.

Coordination with Other Coverage

If you have retiree coverage, union benefits, or a secondary insurance plan, Part B may coordinate with that. But beware:

• Coordination of benefits can delay payment processing.

• Some secondary plans don’t cover excess charges.

• Certain supplemental policies may only cover approved Medicare services.

The timing of claims and how each plan handles cost-sharing can make a huge difference. It’s important to read your plan’s fine print to avoid unexpected charges.

What Happens If You Miss a Timeline

Missing your Initial Enrollment Period (IEP) can result in late enrollment penalties that last for the rest of your life. This applies unless you qualify for a Special Enrollment Period (SEP), such as being covered by employer insurance when you first became eligible.

• IEP: The 7-month window includes the 3 months before, the month of, and 3 months after your 65th birthday.

• GEP: If you miss your IEP, you can sign up during the General Enrollment Period from January 1 to March 31. Your coverage starts July 1, and you may face permanent premium penalties.

In 2025, the late enrollment penalty is 10% of the Part B premium for each full 12-month period you were eligible but didn’t sign up. That can add up quickly.

Income-Based Premium Adjustments in 2025

In addition to standard costs, Medicare Part B premiums are higher if your income exceeds certain thresholds. These Income-Related Monthly Adjustment Amounts (IRMAA) are based on your tax return from two years ago (i.e., your 2023 return for 2025 premiums).

Thresholds for 2025:

• Individuals: $106,000

• Couples (Joint Filers): $212,000

If you cross these limits, you’ll pay an adjusted premium based on a sliding scale. Many beneficiaries are caught off-guard when their premium rises due to a capital gain, IRA withdrawal, or retirement payout from two years prior.

Medical Necessity Isn’t Always Black and White

Even when a treatment or procedure is ordered by your doctor, Medicare may deny it if it doesn’t meet their definition of “medically necessary.”

• You may be responsible for the full cost of a denied service.

• You can appeal, but reimbursement is not guaranteed.

Before undergoing treatment, you should:

• Ask your provider if they believe Medicare will approve it.

• Request a written notice of denial (Advance Beneficiary Notice).

• Understand that preventive and diagnostic services are handled differently.

Preventive Care Isn’t Always Free

Medicare Part B does cover many preventive services like cancer screenings and annual wellness visits without coinsurance. But not everything during the visit may be covered.

You may be billed for:

• Additional labs not included in the standard screening

• Follow-up consultations during the same appointment

• Procedures that go beyond the preventive scope

In short, what starts as a “free” visit can end up on your medical bill.

Your Options to Minimize Surprise Bills

To reduce the risk of surprise costs under Part B, consider the following:

• Always confirm that your provider accepts Medicare assignment.

• Keep track of the services billed during each visit.

• Review your Medicare Summary Notices (MSN) for accuracy.

• Stay within Medicare-covered services unless you’re prepared to pay out-of-pocket.

• Consider supplemental insurance for added protection against cost-sharing.

Understanding the 2025 Limits and Protections

Medicare Part B does not have an out-of-pocket maximum. That’s why your exposure to surprise bills continues, no matter how long you’ve been enrolled. If you undergo extensive outpatient treatments or specialist care, those 20% coinsurance charges can accumulate rapidly.

Some beneficiaries consider adding supplemental policies to reduce financial exposure. These policies can cover:

• Part B coinsurance

• Excess charges

• Additional days of hospitalization

But even with that, understanding what is and isn’t covered remains your best defense.

Why It’s Critical to Reassess Your Coverage Annually

Every year, Medicare coverage rules and premiums are updated. Providers may leave Medicare, new services may be added or excluded, and your health needs may shift. It’s not enough to review your Part D plan during the October 15 to December 7 Annual Enrollment Period—you should reassess your Part B exposure as well.

Use the Annual Notice of Change to:

• See if your providers still accept assignment

• Check updates to covered services

• Review premium and deductible changes

Even if your situation hasn’t changed, Medicare might have.

Surprise Bills Are a Reality—But They Don’t Have to Be Yours

You may be doing everything right and still find Medicare Part B leading to medical bills you didn’t anticipate. The key is to stay proactive, read your plan details thoroughly, and speak with professionals who can walk you through what your coverage truly means.

To avoid costly surprises, speak with a licensed agent listed on this website. They can help you understand how your choices affect your out-of-pocket costs and recommend strategies to fill in the gaps.