What Is Medicare Part D?
Medicare Part D is the prescription drug benefit program established by the Medicare Modernization Act of 2003. It is available to anyone enrolled in Medicare Part A or Part B. Part D coverage is provided through private insurance companies approved by Medicare — not by the federal government directly.
You can get Part D coverage in two ways: through a standalone Prescription Drug Plan (PDP) that works alongside Original Medicare, or through a Medicare Advantage plan that includes drug coverage (MA-PD). In 2026, there are hundreds of Part D plans available across the country, each with different premiums, formularies, and pharmacy networks.
Part D enrollment is voluntary, but delaying enrollment without creditable coverage triggers a permanent late enrollment penalty. If you have Original Medicare without employer or other creditable drug coverage, enrolling in a Part D plan during your Initial Enrollment Period is strongly recommended.
Who Needs Medicare Part D?
Anyone enrolled in Original Medicare who does not have creditable prescription drug coverage from another source should enroll in a Part D plan. Creditable coverage means your existing drug benefit is expected to pay, on average, at least as much as the standard Part D benefit.
Common sources of creditable coverage include employer or retiree health plans, TRICARE, the Federal Employees Health Benefits (FEHB) program, and VA healthcare. Your current plan is required to notify you each year whether its drug coverage is creditable. Keep these notices — you may need them to avoid a late enrollment penalty.
Even if you take few or no prescriptions today, enrolling in a low-cost Part D plan protects you from the late enrollment penalty and ensures coverage if your medication needs change. Prescription costs can rise quickly with a single diagnosis or hospitalization.
How Part D Coverage Works: The Four Phases
Phase 1: Annual Deductible
Most Part D plans charge a deductible before coverage begins. In 2026, the maximum allowable Part D deductible is $590. Some plans have a lower deductible or no deductible at all. During this phase, you pay the full negotiated cost of your prescriptions until you meet the deductible amount.
Phase 2: Initial Coverage
After meeting the deductible, you enter the initial coverage phase. During this phase, you pay a copay or coinsurance for each prescription, and your plan pays the rest. Costs vary by drug tier — generics are the least expensive, while specialty medications carry the highest cost sharing.
Phase 3: Coverage Gap
The coverage gap, historically called the donut hole, begins when combined spending by you and your plan reaches a set threshold. Thanks to the Inflation Reduction Act, the coverage gap is effectively eliminated in 2026. You continue paying standard copays through this phase, and your total out-of-pocket costs are now capped at $2,100 per year.
Phase 4: Catastrophic Coverage
Once your true out-of-pocket spending reaches the $2,100 annual cap, you enter catastrophic coverage. In 2026, this means you pay $0 for all covered Part D drugs for the rest of the calendar year. This cap is a major change from prior years and provides significant financial protection for beneficiaries with high drug costs.
Formulary Tiers Explained
Every Part D plan maintains a formulary — a list of covered medications organized into tiers. Each tier has a different cost-sharing amount. Understanding your plan's formulary is essential because it directly determines what you pay at the pharmacy counter for each prescription.
Most Part D formularies use a five-tier structure. Tier 1 covers preferred generics with the lowest copays, often $0 to $15. Tier 2 covers non-preferred generics at slightly higher costs. Tier 3 includes preferred brand-name drugs. Tier 4 covers non-preferred brand-name medications with higher copays or coinsurance.
Tier 5 is reserved for specialty medications — typically high-cost drugs for complex conditions like cancer, multiple sclerosis, or rheumatoid arthritis. Specialty tier drugs often require coinsurance (a percentage of the cost) rather than a flat copay. Under the 2026 out-of-pocket cap, even beneficiaries on specialty drugs will pay no more than $2,100 total per year.
Extra Help and Low Income Subsidy (LIS)
Medicare Extra Help, also known as the Low Income Subsidy (LIS), is a federal program that helps people with limited income and resources pay for Part D prescription drug costs. Extra Help can cover premiums, deductibles, and copays — saving qualified beneficiaries thousands of dollars each year.
To qualify for Extra Help in 2026, individuals generally must have annual income below approximately $22,590 and countable resources below $17,220. Married couples living together must have combined income below $30,660 and resources below $34,360. Your home, vehicle, burial plots, and life insurance policies do not count as resources.
You can apply for Extra Help through the Social Security Administration online, by phone, or at your local Social Security office. If you qualify for full Extra Help, you pay no Part D premium, no deductible, and minimal copays — typically $0 to $4.50 for generics and $0 to $11.20 for brand-name drugs in 2026.
The $35 Insulin Cap Under the Inflation Reduction Act
The Inflation Reduction Act of 2022 capped out-of-pocket insulin costs at $35 per month per covered insulin product for all Medicare Part D enrollees. This provision, which took effect January 1, 2023, applies regardless of whether you have met your deductible or which coverage phase you are in.
The cap covers all formulary insulins, including vials, pens, and biosimilar insulin products. In 2026, every Part D plan and every Medicare Advantage plan with drug coverage must honor the $35 monthly cap. Beneficiaries do not need to apply or take any special action — the cap is applied automatically at the pharmacy.
For the approximately 3.4 million Medicare beneficiaries who use insulin, this cap provides substantial savings. Prior to the IRA, some beneficiaries paid hundreds of dollars per month for insulin. The $35 cap, combined with the new $2,100 annual out-of-pocket maximum, represents the most significant reduction in Medicare prescription drug costs in the program's history.
The Medicare Prescription Payment Plan: Spreading Out Drug Costs
Since 2025, every Part D plan and every Medicare Advantage plan with drug coverage must offer the Medicare Prescription Payment Plan, sometimes called M3P. It lets you pay your share of prescription costs in monthly installments across the calendar year instead of paying the full amount at the pharmacy counter. There is no fee to join, and the plan charges no interest.
It helps to be clear about what this program does and does not do. The Prescription Payment Plan does not lower the total you pay for your medications — your yearly out-of-pocket total is the same, and it is still limited by the annual Part D out-of-pocket cap. What changes is the timing: instead of a large bill in a single month, you get a monthly statement from your plan that splits your costs into steadier payments.
This option tends to help people who face high drug costs early in the year — for example, someone who fills an expensive specialty medication in January and would otherwise pay much of their annual share all at once. Each year, plans must identify members who are likely to benefit and send them a notice. Taking part is completely voluntary, and you can leave the program at any time.
You can opt in before the plan year begins or at any point during the year by contacting your Part D or Medicare Advantage plan. If spreading your costs into monthly payments would make your budget easier to manage, ask your plan or a licensed Sidebar advisor whether the Prescription Payment Plan is a good fit for you.
How to Choose the Right Part D Plan
Choosing the right Part D plan starts with your medication list. Gather all your current prescriptions, including dosages and quantities, and check each plan's formulary to confirm your drugs are covered. Pay close attention to which tier each medication falls on, because tier placement directly affects your copay.
Next, verify that your preferred pharmacy is in the plan's network. Part D plans negotiate different prices with different pharmacies, and using an out-of-network pharmacy can mean higher costs or no coverage at all. Many plans offer preferred pharmacies with even lower copays than standard in-network pharmacies.
Compare total estimated annual costs, not just the monthly premium. A plan with a higher premium but lower copays on your medications may save you more overall. A licensed Medicare agent can run a personalized cost comparison using your specific drug list and preferred pharmacy to identify the plan with the lowest total annual cost.