Medicare Part C and Part D are two ways to get additional coverage beyond Original Medicare. Part C (Medicare Advantage) bundles your hospital and medical coverage into a single private plan, often with extras like dental and vision. Part D covers prescription drugs. They work differently, cost differently, and you can sometimes get both in one plan.
How Part C (Medicare Advantage) Works
Medicare Advantage is a private insurance plan that replaces Original Medicare. When you enroll, a private company approved by Medicare takes over delivery of all your Part A (hospital) and Part B (medical) benefits. You still have Medicare, but your coverage flows through the private plan instead of directly through the federal government.
Most Medicare Advantage plans also include benefits that Original Medicare doesn’t cover: vision, hearing, dental, and fitness programs are common additions. These extras vary by plan and by region, so what’s available in one zip code may not exist in another.
The trade-off for these extras is typically a more restricted provider network. Medicare Advantage plans come in two main structures:
- HMO plans require you to use in-network providers for covered services. If you see a doctor outside the network, the plan may not cover any of the cost.
- PPO plans also have a preferred network but will cover out-of-network care at a higher cost to you.
This is one of the biggest practical differences between Original Medicare and Medicare Advantage. With Original Medicare, you can see any provider in the country who accepts Medicare. With an Advantage plan, your choices are narrower, especially with an HMO.
Part C Costs and Out-of-Pocket Limits
Many Medicare Advantage plans charge a $0 monthly premium on top of your Part B premium, though this varies. Where Advantage plans offer a real financial safeguard is the annual out-of-pocket maximum. Original Medicare has no cap on what you can spend in a year, but Medicare Advantage plans do.
In 2025, the out-of-pocket limit for in-network services on a Medicare Advantage plan cannot exceed $9,350. For plans that include out-of-network coverage, the combined in-network and out-of-network cap is $14,000. Once you hit that ceiling, the plan pays 100% of covered services for the rest of the year. Many plans set their limits well below these maximums, so it’s worth comparing.
How Part D (Prescription Drug Coverage) Works
Part D helps pay for the brand-name and generic medications you pick up at a pharmacy. It’s optional, offered exclusively through private insurance companies approved by Medicare. Every Part D plan has a formulary, which is its list of covered drugs. The drugs on that list, and what you pay for each one, differ from plan to plan.
You can get Part D coverage in two ways. If you stay on Original Medicare, you add a standalone Prescription Drug Plan (PDP) to your coverage. If you choose a Medicare Advantage plan, many of those plans bundle drug coverage right in (these are called MA-PD plans). You cannot have both a standalone drug plan and drug coverage through Medicare Advantage at the same time.
There’s a meaningful financial difference between these two paths. Medicare Advantage plans have access to additional funding (called rebates) that standalone drug plans don’t receive. This allows Advantage plans to offer richer drug benefits or lower premiums for prescription coverage. Standalone drug plans set their premiums based entirely on the cost of the drug benefit itself.
The $2,000 Out-of-Pocket Cap on Drugs
Starting in 2025, the Inflation Reduction Act introduced a $2,000 annual cap on what you pay out of pocket for prescription drugs under Part D. This applies to all Part D plans, whether standalone or bundled into a Medicare Advantage plan. Once your out-of-pocket drug spending reaches $2,000 in a calendar year, you pay nothing more for covered prescriptions for the rest of that year.
This is a major change. Before 2025, people taking expensive medications could face thousands of dollars in annual drug costs with no hard ceiling. The new cap makes drug spending far more predictable.
Eligibility and Enrollment
To join either Part C or Part D, you need to already have Medicare. For Part D specifically, you must have Part A or Part B (or both), live in the plan’s service area, be a U.S. citizen or lawfully present in the country, and enroll during a valid enrollment period.
Medicare Advantage has similar requirements: you need both Part A and Part B and must live in the plan’s service area. The main enrollment window for both Part C and Part D is the Annual Election Period, which runs from October 15 through December 7 each year for coverage starting January 1.
The Part D Late Enrollment Penalty
If you don’t sign up for Part D when you’re first eligible and you go 63 days or more without creditable drug coverage (coverage that’s at least as good as a standard Part D plan), you’ll face a permanent penalty. The penalty adds 1% of the national base beneficiary premium for every month you went without coverage. In 2026, that base premium is $38.99, so each uncovered month adds roughly 39 cents per month to your premium.
That sounds small, but it compounds. If you waited two years (24 months) without coverage, your penalty would be 24% of the base premium, or about $9.36 extra per month, every month, for as long as you have Part D. The penalty amount recalculates each year as the base premium changes, so it generally grows over time.
Income-Based Surcharges on Part D
Higher-income beneficiaries pay an extra monthly amount on top of their Part D premium. For 2025, individual filers earning $106,000 or less (or joint filers earning $212,000 or less) pay no surcharge. Above those thresholds, the surcharge increases in steps:
- $106,001 to $133,000 individual / $212,001 to $266,000 joint: $13.70 per month
- $133,001 to $167,000 individual / $266,001 to $334,000 joint: $35.30 per month
- $167,001 to $200,000 individual / $334,001 to $400,000 joint: $57.00 per month
- $200,001 to $499,999 individual / $400,001 to $749,999 joint: $78.60 per month
- $500,000 or more individual / $750,000 or more joint: $85.80 per month
These surcharges are based on your tax return from two years prior. If your income has dropped since then due to retirement or another life event, you can appeal to Social Security for a reduction.
Choosing Between Part C and Standalone Part D
The core decision comes down to how you want your Medicare structured. If you prefer maximum flexibility in choosing doctors and hospitals, Original Medicare with a standalone Part D plan (and possibly a Medigap supplement) keeps your options open. You can see any Medicare-accepting provider nationwide without referrals or network restrictions.
If you want lower premiums, extra benefits like dental and vision, and a single plan managing everything, Medicare Advantage with built-in drug coverage simplifies things. The trade-off is a narrower provider network and potential requirements like prior authorization for certain services. People who travel frequently, split time between states, or have established relationships with specialists in different health systems often find Original Medicare more practical. People who stay local and want predictable, bundled coverage often prefer Medicare Advantage.