Medicare Part B is the “medical insurance” half of Original Medicare. It covers outpatient care: doctor visits, lab tests, preventive screenings, and medical equipment you use at home. While Part A handles hospital stays, Part B picks up nearly everything else you’d encounter in a doctor’s office, outpatient clinic, or ambulance. In 2025, the standard monthly premium is $185.00, with an annual deductible of $257 before cost-sharing kicks in.
What Part B Covers
Part B pays for two broad categories of care. The first is medically necessary services, meaning anything that meets accepted standards of medical practice to diagnose or treat a condition. The second is preventive services designed to catch illness early or stop it from developing.
In practical terms, that includes:
- Doctor and specialist visits in offices and outpatient clinics
- Outpatient surgeries, including same-day procedures
- Lab tests and diagnostic imaging like X-rays, MRIs, and CT scans
- Emergency and observation services, even when they involve an overnight hospital stay classified as outpatient
- Mental health care, including partial hospitalization programs and intensive outpatient programs for mental health conditions and substance use disorders
- Medical supplies like splints, casts, and certain injectable drugs given during a procedure
- Ambulance services when other transportation would endanger your health
- Durable medical equipment such as wheelchairs, walkers, hospital beds, and oxygen equipment
For durable medical equipment to be covered, it must be ordered by your doctor, used in your home, and be the type of item that’s only useful to someone who is sick or injured. The equipment also needs to be built to withstand repeated use and expected to last at least three years. You’ll want to confirm that any equipment supplier is enrolled in Medicare and accepts assignment before placing an order, because a non-participating supplier can charge you more than the Medicare-approved amount.
Preventive Services at No Cost
One of the most valuable features of Part B is its preventive care coverage. You pay nothing for most preventive services as long as your provider accepts assignment (agrees to charge only the Medicare-approved amount). This zero-cost coverage applies to a wide range of screenings and shots.
Covered preventive services include screening mammograms, colonoscopies and other colorectal cancer screenings, lung cancer screenings, cardiovascular disease screenings, diabetes screenings, depression screenings, glaucoma tests, and prostate cancer screenings. Part B also covers hepatitis B and C screenings, HIV screenings, sexually transmitted infection screenings, and bone density measurements.
Vaccines are covered too: flu shots, COVID-19 vaccines, pneumococcal shots, and hepatitis B shots. Part B also pays for a one-time “Welcome to Medicare” preventive visit when you first enroll, plus a yearly wellness visit after that. For people managing chronic conditions, it covers diabetes self-management training, medical nutrition therapy, obesity behavioral therapy, and tobacco cessation counseling.
What Part B Costs in 2025
Most people pay $185.00 per month for Part B in 2025. This applies to individuals earning $106,000 or less, or couples filing jointly with income of $212,000 or less. The premium is typically deducted automatically from your Social Security check.
If your income is higher, you’ll pay an additional surcharge called IRMAA (Income-Related Monthly Adjustment Amount). The surcharges for 2025 are based on your tax return from two years prior and break down as follows for individual filers:
- $106,001 to $133,000: $259.00 per month
- $133,001 to $167,000: $370.00 per month
- $167,001 to $200,000: $480.90 per month
- $200,001 to $499,999: $591.90 per month
- $500,000 or more: $628.90 per month
For joint filers, double each income threshold. So a couple filing jointly would pay the standard $185.00 as long as their combined income stays at or below $212,000.
Beyond the monthly premium, there’s an annual deductible you must meet before Part B starts paying. After you’ve met the deductible, you typically pay 20% of the Medicare-approved amount for covered services. That 20% coinsurance applies to most Part B services, from doctor visits to outpatient procedures to medical equipment.
What Part B Does Not Cover
Part B has some notable gaps. It does not cover most dental care, including routine cleanings, fillings, tooth extractions, or dentures. Routine eye exams for prescription glasses are excluded, as are hearing aids and the exams needed to fit them. Long-term care, cosmetic surgery, and massage therapy fall outside Part B as well.
Routine physical exams are also not covered, which sometimes confuses people. The yearly wellness visit (which is covered) focuses on creating or updating a personalized prevention plan. It is not a head-to-toe physical. If your doctor performs additional diagnostic tests during the visit, those tests may trigger separate charges.
When to Sign Up
Your initial enrollment period for Part B is a seven-month window centered on the month you turn 65. It starts three months before your birthday month and ends three months after it. If you’re already receiving Social Security benefits, you’ll be enrolled automatically. Otherwise, you need to sign up actively.
Missing this window has real financial consequences. If you delay enrollment without qualifying for a special enrollment period (which generally applies if you’re still covered through an employer), you’ll face a late enrollment penalty that lasts for as long as you have Part B. The penalty adds 10% to your monthly premium for every full 12-month period you could have signed up but didn’t. Someone who waited two years past their enrollment window, for example, would pay a 20% surcharge on top of the standard premium for the rest of their time on Medicare. That penalty never goes away.
How Part B Fits Into Original Medicare
Part B works alongside Part A to form Original Medicare. Part A covers inpatient hospital stays, skilled nursing facility care, and hospice. Part B covers virtually everything on the outpatient side. Together, they still leave you responsible for premiums, deductibles, and the 20% coinsurance on Part B services, with no annual cap on out-of-pocket spending. That open-ended 20% is why many people add a Medigap (Medicare Supplement) policy or choose a Medicare Advantage plan (Part C) as an alternative that bundles Part A and Part B coverage with out-of-pocket limits built in.