Medicare Part B pays for 80% of outpatient medical costs after you meet a $283 annual deductible, but there is no yearly limit on the 20% you must cover out-of-pocket. This article explains the 2026 Part B premium, the 80/20 cost-sharing structure, free preventive services, and a critical trap: if your provider doesn't accept "assignment," you could be charged up to 15% more than the Medicare-approved amount.
The Part B Premium and Deductible
For 2026, the standard monthly premium for Medicare Part B is expected to be around $174.70 (final figure pending). You pay this premium directly to Medicare unless you receive Social Security benefits, in which case it is typically deducted. The annual deductible is $283. Once you meet this deductible, Medicare begins sharing costs.
The 80/20 Rule — and the Missing Cap
Part B uses an 80/20 coinsurance split: Medicare pays 80% of the Medicare-approved amount for covered services, and you pay the remaining 20%. Unlike many private insurance plans, there is no annual out-of-pocket maximum. This means if you have a serious illness or need expensive outpatient treatments, your 20% share could add up to thousands of dollars with no safety net.
What Part B Actually Covers
Part B covers medically necessary outpatient services, including doctor visits, lab tests, X-rays, durable medical equipment (like walkers or wheelchairs), mental health services, ambulance transportation, and outpatient hospital care. It also covers preventive services listed below.
Free Preventive Services
Part B offers many preventive services with no cost-sharing (no deductible or coinsurance) if you see a provider who accepts assignment. These include:
- Annual wellness visit
- Cardiovascular screenings
- Cancer screenings (mammograms, colonoscopies, etc.)
- Flu and pneumonia shots
- Diabetes screenings and self-management training
The Assignment Trap
When you see a doctor or other health care provider, they may charge more than the Medicare-approved amount. If the provider accepts "assignment," they agree to accept Medicare's payment as full payment. If they do not (a "non-participating" provider), they can charge you up to 15% more than Medicare's approved amount — this is called the "limiting charge." You are responsible for the full 20% coinsurance plus this extra 15% surcharge, which can significantly increase your out-of-pocket costs. Always check whether a provider accepts assignment before receiving care.
Next Steps
Understanding these rules is essential to avoid unexpected bills. Consider whether a Medicare Supplement (Medigap) policy or a Medicare Advantage plan might better protect you from the 20% gap and the assignment trap.