In 2025, Part B has a one-time annual deductible of $257. You are required to pay this amount in full before Part B begins covering services. Once the deductible is met, Part B provides 80/20 coverage, meaning it covers 80% of the Medicare Allowable Charge while you are responsible for the remaining 20%. A significant drawback to Part B is that the 20% cost-sharing does not have an upper limit.