Medicare Part B in 2025: What It Costs and What It Covers

Medicare Part B is the second piece of Original Medicare, and for most beneficiaries it's the one that gets used most often. While Part A covers hospital stays and inpatient care, Part B is what pays when you walk into a doctor's office, get a lab test, receive chemotherapy, or need an MRI. Understanding exactly what Part B covers, what it costs, and how its cost-sharing structure works is essential before you make any enrollment decision — because the choices you make at 65 can follow you financially for the rest of your life.

The standard monthly premium for Medicare Part B in 2025 is $185.00. For most beneficiaries, this amount is automatically deducted from their Social Security check each month, which means you never write a check — it simply reduces what lands in your bank account. But that $185.00 figure is only the starting point. Before Part B pays a single dollar of your medical bills, you must first meet the annual deductible, which is $257 in 2025. Once you've paid that deductible out of pocket, Part B kicks in and covers 80% of Medicare-approved costs for covered services. You are responsible for the remaining 20% — and critically, there is no annual out-of-pocket maximum under Original Medicare alone. If you have a serious illness requiring frequent specialist visits, imaging, or outpatient procedures, that 20% coinsurance can accumulate into thousands of dollars over the course of a year.

Not everyone pays the same Part B premium. The federal government uses a system called IRMAA — the Income-Related Monthly Adjustment Amount — to charge higher premiums to beneficiaries whose income exceeds certain thresholds. In 2025, IRMAA surcharges kick in for individuals with modified adjusted gross income above $106,000 (or $212,000 for married couples filing jointly). At the highest income tier, individuals with MAGI above $500,000 pay a total monthly Part B premium of $628.90. These surcharges are based on your tax return from two years prior, so your 2025 premium is calculated using your 2023 income. If your income has dropped significantly since then — due to retirement, the death of a spouse, or another life-changing event — you can file Form SSA-44 with the Social Security Administration to request a reduction based on more recent income. This is a step many beneficiaries don't know they can take, and it can result in meaningful monthly savings.

Data Snapshot: According to CMS.gov data, Medicare Part B enrolled approximately 67.3 million beneficiaries as of 2024, making it one of the largest health insurance programs in the world. CMS also reports that the average Part B premium has risen from $148.50 in 2021 to $185.00 in 2025 — a 24.6% increase over four years — underscoring why understanding premium trajectory matters when planning retirement healthcare budgets. CMS data further shows that roughly 8% of Part B enrollees are subject to IRMAA surcharges in any given year, meaning the vast majority pay the standard rate, but those who do face surcharges often encounter them as an unwelcome surprise.

What does Part B actually cover? The list is broader than many people expect. Part B covers two main categories: medically necessary services and preventive services. Medically necessary services include doctor visits (both primary care and specialists), outpatient surgery, emergency room visits that don't result in a hospital admission, ambulance transportation, durable medical equipment like wheelchairs and walkers, mental health services, physical and occupational therapy, and most outpatient diagnostic tests including X-rays, MRIs, and lab work. Preventive services covered at no cost to you — meaning no deductible and no coinsurance — include an annual wellness visit, cardiovascular disease screenings, colorectal cancer screenings, diabetes screenings, mammograms, bone density tests, and certain vaccines including flu shots and hepatitis B. The key distinction is that these preventive services are free only when your doctor bills them as preventive. If your annual wellness visit turns into a discussion of a new symptom or a chronic condition, that portion of the visit may be billed as a regular office visit and subject to the 20% coinsurance.

One of the most important — and frequently misunderstood — aspects of Part B is what it does not cover. Part B does not cover prescription drugs you take at home. Those are covered under a separate program, Medicare Part D, which requires its own enrollment and premium. Part B also does not cover routine dental care, routine vision exams or eyeglasses, hearing aids, or most long-term custodial care. This is a significant gap for many seniors, because dental and hearing costs can be substantial. If you need a hearing aid, which can cost $3,000 to $7,000 per pair out of pocket, Part B will not help. Some Medicare Advantage plans (Part C) do include dental, vision, and hearing benefits, which is one reason many beneficiaries choose to leave Original Medicare for an Advantage plan — though that trade-off comes with its own network restrictions and prior authorization requirements worth examining carefully.

Enrollment timing for Part B is one of the most consequential decisions you'll face at 65. Your Initial Enrollment Period (IEP) is a seven-month window that begins three months before the month you turn 65, includes your birthday month, and extends three months after. If you enroll during the first three months of your IEP, your coverage starts on the first day of your birthday month. If you wait until your birthday month or after, your coverage start date is delayed by one to three months. If you miss your IEP entirely and don't have qualifying employer coverage, you'll face a late enrollment penalty: a permanent 10% increase in your Part B premium for every 12-month period you went without coverage. That penalty never goes away. A beneficiary who delays enrollment for three years, for example, would pay a 30% premium surcharge for the rest of their life — on top of whatever the standard premium happens to be each year.

There is an important exception to the late enrollment penalty: if you or your spouse is still working and you're covered under an employer group health plan based on active employment, you can delay Part B without penalty. When that employment ends, you have an eight-month Special Enrollment Period to sign up for Part B without facing a late penalty. Note carefully: COBRA coverage and retiree health coverage do not count as active employer coverage for this purpose. If you retire and go on COBRA, your eight-month SEP clock starts ticking from the date your active employment ended — not from when your COBRA runs out. Many beneficiaries make this mistake and end up with a gap in coverage or an unexpected penalty.

For beneficiaries who want to reduce or eliminate the 20% coinsurance exposure under Part B, there are two main paths. The first is a Medicare Supplement plan, also called Medigap. These are standardized private insurance policies sold in most states under letter designations (Plan G, Plan N, Plan F, etc.). Plan G, the most popular option for new enrollees since 2020, covers the Part B coinsurance and excess charges after you pay the Part B deductible yourself. In 2025, average monthly premiums for Plan G range from roughly $100 to $200 depending on your age, gender, location, and the insurance company — though prices vary widely and shopping multiple carriers is essential. The second path is Medicare Advantage (Part C), which replaces Original Medicare with a private plan that typically includes an out-of-pocket maximum, often ranging from $4,000 to $8,850 in 2025, providing a ceiling on your annual exposure that Original Medicare alone does not offer.

If you're already enrolled in Part B and believe you're paying too much — either because of an IRMAA surcharge based on outdated income, or because you enrolled late and are carrying a penalty — there are formal appeal processes available. For IRMAA, file SSA-44 with your local Social Security office and provide documentation of the qualifying life event that reduced your income. For late enrollment penalties, the appeals process is more limited, but errors in CMS records can sometimes be corrected. Contacting your State Health Insurance Assistance Program (SHIP) counselor is a smart first step — SHIP counselors provide free, unbiased help navigating Medicare enrollment issues and are available in every state. You can find your local SHIP contact at shiphelp.org.

Finally, it's worth understanding how Part B interacts with the rest of your Medicare coverage on a day-to-day basis. When you see a doctor who accepts Medicare assignment — meaning they agree to accept Medicare's approved amount as full payment — you pay 20% of that approved amount after your deductible. When you see a doctor who does not accept assignment but still sees Medicare patients (called a non-participating provider), they can charge up to 15% above the Medicare-approved amount, and you may owe that excess charge on top of your 20% coinsurance. A small number of doctors have completely opted out of Medicare and can charge whatever they choose — in that case, Medicare pays nothing, and you're responsible for the entire bill. Before seeing any new provider, it's worth confirming their Medicare participation status at medicare.gov/care-compare, which lets you search doctors, hospitals, and other providers by name or location.