What Is Medicare Part B?
Medicare Part B is the medical insurance portion of Original Medicare. While Part A covers hospital and facility care, Part B covers the services you receive outside of a hospital — doctor visits, lab tests, imaging, outpatient procedures, preventive care, and durable medical equipment.
Unlike Part A, Part B always has a monthly premium. Most people pay the standard premium, which is $185.00/month in 2025. Higher-income beneficiaries pay more through an IRMAA surcharge — use our IRMAA Calculator to check your amount.
What Does Medicare Part B Cover?
Medically Necessary Services
Part B covers services and supplies that are medically necessary to diagnose or treat a medical condition. This broad category includes:
- Doctor visits (primary care and specialists)
- Outpatient hospital services and surgery
- Emergency room visits (when not admitted as inpatient)
- Ambulance services
- Mental health services (outpatient)
- Physical, occupational, and speech therapy
- Durable medical equipment (wheelchairs, walkers, oxygen, CPAP machines)
- Lab tests, X-rays, and other diagnostic imaging
- Second surgical opinions
- Kidney dialysis
Preventive Services (Most at No Cost)
One of Part B's most valuable features is coverage for a wide range of preventive services at no cost to you — no deductible, no 20% coinsurance — as long as you see a Medicare-accepting provider:
- "Welcome to Medicare" preventive visit (one-time, within first 12 months of Part B)
- Annual Wellness Visit (every 12 months after first year)
- Mammograms (annual)
- Colorectal cancer screenings
- Cardiovascular disease screenings
- Diabetes screenings and self-management training
- Depression screening
- Flu, pneumococcal, COVID-19, and Hepatitis B vaccines
- Bone density measurement
What Does Medicare Part B Cost in 2025?
| Cost Type | Amount (2025) | Notes |
|---|---|---|
| Monthly Premium | $185.00 | Standard; higher earners pay IRMAA surcharge |
| Annual Deductible | $257 | You pay this first before Medicare starts paying |
| Coinsurance | 20% of approved amount | After deductible; no annual out-of-pocket cap in Original Medicare |
| Late Enrollment Penalty | 10% per year delayed | Added to your premium permanently |
The Part B Late Enrollment Penalty
If you don't sign up for Part B when you are first eligible, and you don't have a valid reason to delay (see Special Enrollment Period below), you will face a late enrollment penalty. The penalty is 10% of the standard Part B premium for every 12-month period you could have had Part B but chose not to enroll.
This penalty is permanent — it is added to your monthly premium for as long as you have Part B.
| Years Delayed | Penalty Amount | Your Monthly Premium (2025 rates) |
|---|---|---|
| 0 (on time) | None | $185.00 |
| 1 year late | 10% | $203.50 |
| 2 years late | 20% | $222.00 |
| 5 years late | 50% | $277.50 |
When to Enroll in Part B
Initial Enrollment Period (IEP)
Your IEP is a 7-month window: 3 months before your 65th birthday month, your birthday month, and 3 months after. This is your primary enrollment window. Enrolling in the first 3 months ensures your coverage starts on the first day of your birth month.
Special Enrollment Period (SEP) — If You Have Employer Coverage
If you or your spouse are still actively working when you turn 65 and you have health coverage through that employer, you may delay Part B enrollment without penalty. You then have a Special Enrollment Period: you can enroll any time while you still have that coverage, or up to 8 months after you lose the coverage or stop working — whichever comes first.
General Enrollment Period (GEP)
If you missed your IEP and don't qualify for a SEP, you can enroll during the General Enrollment Period from January 1 through March 31 each year. Your coverage begins July 1. However, you will owe the late enrollment penalty.