Medicare cost share refers to the portion of your healthcare expenses that you pay out of your own pocket, even after Medicare covers its part. These costs come in three forms: deductibles (a fixed amount you pay before coverage kicks in), coinsurance (a percentage of each service you split with Medicare), and copayments (a flat fee per visit or service). Understanding how these work across different parts of Medicare can save you from unexpected bills.
How Part A Cost Sharing Works
Part A covers hospital stays, skilled nursing facility care, and hospice. The biggest cost-share hit comes at the door: in 2025, the Part A deductible is $1,676 per benefit period. A benefit period starts when you’re admitted to a hospital and ends once you’ve been out for 60 consecutive days. If you’re hospitalized twice within the same benefit period, you pay the deductible only once. But if those stays fall in separate benefit periods, you pay it again.
For the first 60 days of a hospital stay, Medicare covers everything beyond the deductible. After that, daily coinsurance charges start climbing. Days 61 through 90 cost you $419 per day. If you need to stay beyond 90 days, Medicare draws from a pool of 60 “lifetime reserve days” at $838 per day, and once those are used up, they’re gone for good. For skilled nursing facility care, Medicare covers the first 20 days fully. Days 21 through 100 carry a $209.50 daily coinsurance charge.
How Part B Cost Sharing Works
Part B handles doctor visits, outpatient care, medical equipment, and preventive services. You pay a standard monthly premium of $185 in 2025 and an annual deductible of $257. After you meet that deductible, the cost-sharing formula is straightforward: you pay 20% of the Medicare-approved amount for most covered services, and Medicare pays the other 80%.
That 20% applies broadly. It covers outpatient hospital care, inpatient doctor services during a hospital stay, outpatient mental health visits, and durable medical equipment like wheelchairs, walkers, and hospital beds. The key detail is that this coinsurance is based on the “Medicare-approved amount,” not whatever a provider might charge. When your doctor “accepts assignment,” they agree to take that approved amount as full payment, which protects you from being billed the difference.
One critical gap in Original Medicare: there is no yearly limit on what you pay out of pocket for Part B services. If you have a year with major medical needs, that 20% coinsurance can add up without a ceiling. This is one of the main reasons people buy supplemental coverage.
Part D Prescription Drug Costs
Part D covers prescription medications, and its cost-sharing structure has multiple stages: a deductible, then copayments or coinsurance that vary by drug tier, followed by a coverage gap. The good news is that starting in 2025, a new annual cap limits your total out-of-pocket drug spending to no more than $2,000. Once you hit that threshold, you pay nothing for covered prescriptions for the rest of the year. This cap, created by the Inflation Reduction Act, is a major change from prior years when drug costs could spiral much higher.
Medicare Advantage Out-of-Pocket Limits
Medicare Advantage plans (Part C) are private insurance alternatives that bundle Part A, Part B, and usually Part D into one plan. They’re required to cover everything Original Medicare covers, but they structure cost sharing differently, often using flat copayments instead of percentage-based coinsurance.
The biggest advantage from a cost-sharing perspective is that these plans must include an annual out-of-pocket maximum, something Original Medicare lacks entirely. In 2025, that cap cannot exceed $9,350 for in-network services or $14,000 when out-of-network services are included. In practice, the average limit for enrollees is around $5,320 for in-network care. Once you reach your plan’s limit, the plan covers 100% of your costs for the rest of the year.
How Medigap Reduces Your Share
If you stick with Original Medicare and want protection from uncapped cost sharing, Medigap (Medicare Supplement Insurance) policies fill the gaps. These plans are designed specifically to cover your share of costs under Parts A and B, including copayments, coinsurance, and deductibles. A comprehensive Medigap plan can reduce your out-of-pocket exposure to near zero for covered services, though you’ll pay a monthly premium for the policy itself.
Medigap plans are standardized by letter (Plan A, Plan G, Plan N, etc.), and each letter covers a specific combination of cost-sharing expenses. They only work with Original Medicare, not with Medicare Advantage. You typically get the best rates and guaranteed acceptance if you enroll during the six-month window that starts when you first sign up for Part B at age 65 or older.
Income-Based Premium Adjustments
Most people pay the standard $185 monthly premium for Part B. But if your modified adjusted gross income from two years prior exceeds certain thresholds, you’ll pay a surcharge called IRMAA (Income-Related Monthly Adjustment Amount). This surcharge also applies to Part D premiums. The adjustment is tiered, so higher income means a larger surcharge. It’s based on your tax return from two years ago, so your 2023 income determines your 2025 premiums.
Financial Help With Cost Sharing
If your income is limited, Medicare Savings Programs can pay some or all of your cost-sharing expenses. The Qualified Medicare Beneficiary (QMB) program is the most comprehensive. It covers your Part A and Part B premiums, deductibles, coinsurance, and copayments. To qualify as an individual, your monthly income generally needs to be below $1,350 with resources under $9,950 (limits are higher for married couples and for residents of Alaska and Hawaii).
Two other programs cover narrower slices. The Specified Low-Income Medicare Beneficiary (SLMB) program pays your Part B premium if your monthly income is under $1,616 as an individual. The Qualifying Individual (QI) program does the same at a slightly higher income threshold of $1,816 per month. Both have the same resource limit of $9,950 for individuals. Your state Medicaid office handles applications for all three programs, and some states set their income limits higher than the federal floor.