Medicare Part C and Part D are two ways to get additional coverage beyond Original Medicare. Part C (Medicare Advantage) is a bundled alternative to Original Medicare offered by private insurers, covering hospital and medical services plus often prescription drugs. Part D is specifically prescription drug coverage, also delivered through private companies approved by Medicare. Many people encounter both at the same time because most Medicare Advantage plans include Part D drug coverage built in.
What Medicare Part C Covers
Medicare Advantage, officially called Part C, is a Medicare-approved plan from a private insurance company that replaces Original Medicare (Parts A and B). Instead of the government paying your claims directly, you get your benefits through the private plan. These plans must cover every medically necessary service that Original Medicare covers, so you’re not giving up any core benefits by switching.
The real draw for many people is what Part C adds on top. Most Medicare Advantage plans offer extra benefits that Original Medicare doesn’t cover, including vision, hearing, and dental care. Some plans also include gym memberships, transportation to medical appointments, or over-the-counter health product allowances. The specifics vary widely by plan and by region, so two Medicare Advantage plans in the same zip code can look very different.
Most Medicare Advantage plans also bundle in Part D prescription drug coverage, making them what’s known as MA-PD plans. This means you get hospital coverage, doctor visits, and prescription drugs all through a single plan with one card and one premium. HMO and PPO Medicare Advantage plans almost always include drug coverage, and if they do, you can’t buy a separate Part D plan alongside them. Special Needs Plans are required to include drug coverage. Medical Savings Account plans are the exception: they never include drug coverage, so you’d need a standalone Part D plan if you choose one.
What Medicare Part D Covers
Part D is Medicare’s prescription drug benefit. It helps pay for both brand-name and generic medications. Like Part C, Part D is delivered entirely through private insurance companies approved by Medicare. It’s optional, and it’s available to everyone who has Medicare.
If you stick with Original Medicare rather than switching to a Medicare Advantage plan, you can add drug coverage by enrolling in a standalone Part D plan. If you join a Medicare Advantage plan that already includes drug coverage, that plan handles your Part D benefit directly.
How Part D Drug Costs Work
Part D plans use a tier system to organize which drugs they cover and how much you’ll pay for each one. Every plan maintains a formulary, which is its list of covered medications. Drugs placed on lower tiers cost you less, while higher-tier drugs come with bigger copays or coinsurance.
- Tier 1 (lowest cost): Most generic prescription drugs
- Tier 2 (medium cost): Preferred brand-name drugs
- Tier 3 (higher cost): Non-preferred brand-name drugs
- Specialty tier (highest cost): Very high-cost prescription drugs
Each plan can structure its tiers slightly differently, and the same medication might sit on different tiers depending on the plan. This is why checking whether your specific medications are on a plan’s formulary, and which tier they fall under, matters more than just comparing monthly premiums.
The $2,000 Out-of-Pocket Cap
Part D plans used to have a coverage gap, commonly called the “donut hole,” where you’d pay a larger share of drug costs after hitting a certain spending threshold. Starting in 2025, the Inflation Reduction Act eliminated that coverage gap entirely. In its place, there’s now an annual out-of-pocket cap of $2,000. Once your total out-of-pocket drug spending reaches $2,000 in a calendar year, you won’t owe anything more for covered prescriptions for the rest of that year. This is a significant change for people who take expensive medications, since there was previously no hard cap on what you could spend.
Eligibility and Enrollment
To enroll in a Part D drug plan, you need to have Medicare Part A or Part B (or both), live in the plan’s service area, and be a U.S. citizen or lawfully present in the country. Part C has similar requirements. You’ll need to enroll during a valid election period.
The main window for making changes is the Annual Open Enrollment Period, which runs from October 15 through December 7 each year. During this time, you can join a Medicare Advantage plan, switch between Medicare Advantage plans, drop Medicare Advantage and return to Original Medicare, or join or switch standalone Part D plans. Coverage for changes made during this period begins January 1 of the following year.
The Late Enrollment Penalty for Part D
If you don’t sign up for Part D when you’re first eligible and you go 63 days or more without what Medicare considers “creditable” drug coverage (meaning coverage 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 might sound small, but it compounds. If you waited two full years (24 months) without creditable coverage, you’d pay an extra 24% of the base premium every month. And the penalty doesn’t go away. It’s added to your Part D premium for as long as you have Medicare drug coverage, even if you switch plans later. The base premium also changes annually, so the dollar amount of your penalty can increase over time.
If you have drug coverage through an employer, a union, or another source that’s considered creditable, you won’t face the penalty when you eventually enroll. The key is making sure you have documentation that your previous coverage met Medicare’s standard.
Choosing Between Standalone Part D and Medicare Advantage
Your decision between a standalone Part D plan and a Medicare Advantage plan with built-in drug coverage depends on how you want your overall Medicare to work. With Original Medicare plus a standalone Part D plan, you can see any doctor or hospital that accepts Medicare anywhere in the country, and you can add a Medigap supplemental policy to help cover deductibles and coinsurance. But you’ll manage two or three separate plans.
With a Medicare Advantage plan that includes Part D, everything is consolidated into one plan. You’ll typically pay lower premiums (some plans charge $0 beyond your Part B premium), and you get the extra benefits like dental and vision. The tradeoff is that most Medicare Advantage plans use provider networks. HMOs require you to use in-network doctors and get referrals for specialists. PPOs give more flexibility to go out of network but at higher costs. If your preferred doctors aren’t in a plan’s network, or if you travel frequently and want unrestricted access to providers, Original Medicare with a standalone Part D plan may be the better fit.