Nearly everyone enrolled in Medicare is eligible for Part D prescription drug coverage. There’s no income test, no health screening, and no prescription history required. If you have Medicare Part A, Part B, or both, you qualify to join a Part D plan. The real question for most people isn’t whether they’re eligible, but when and how to enroll without paying extra.
The Basic Eligibility Requirements
Part D eligibility comes down to two things: you must be enrolled in Medicare Part A or Part B (or both), and you must live in the service area of the plan you want to join. That’s it. Unlike some government programs, Part D has no income limit or asset test for basic eligibility. Whether you’re 65 and newly retired or 40 with a qualifying disability, you can sign up.
One important restriction: if you’re enrolled in a Medicare Advantage plan that already includes drug coverage (sometimes called an MA-PD plan), you can’t also buy a separate standalone Part D plan. You’d need to drop your Medicare Advantage plan and return to Original Medicare first, at which point you could enroll in a standalone Part D plan.
When to Enroll
Your first chance to sign up is during your Initial Enrollment Period, a seven-month window that starts three months before your Medicare coverage begins and ends three months after. If you request to join a plan before your Part A or Part B start date, your drug coverage kicks in on the same day your Medicare starts. If you enroll after that date, coverage begins the first of the month after the plan receives your request.
If you miss that window, you can enroll during the Annual Open Enrollment Period, which runs from October 15 through December 7 each year. Coverage for plans chosen during open enrollment starts January 1 of the following year.
Special Enrollment Periods
Certain life changes open a window to enroll or switch plans outside the usual schedule. These include moving to a new area where different plans are available, losing employer or union drug coverage, losing Medicaid eligibility, being released from incarceration, or having your current plan’s contract with Medicare terminated. If you qualify for both Medicare and Medicaid, or if you receive Extra Help with drug costs, you can change plans once per quarter.
What Happens If You Don’t Enroll on Time
Delaying enrollment carries a financial penalty unless you have other coverage that’s at least as comprehensive as Part D. This is called “creditable coverage,” and it means the plan is expected to pay, on average, at least as much as a standard Medicare drug plan. Many employer and union plans qualify, and your plan is required to notify you each year whether its coverage is creditable.
If you go 63 days or more without creditable drug coverage and later decide to enroll in Part D, you’ll pay a late enrollment penalty of 1% of the national base beneficiary premium for every month you were uncovered. In 2026, that base premium is $38.99, so each uncovered month adds roughly 39 cents per month to your premium, permanently. That might sound small, but it compounds quickly. Someone who waited two years without coverage would pay about $9.36 more per month for the rest of the time they have Part D.
Financial Help Through Extra Help (LIS)
While everyone with Medicare can enroll in Part D, lower-income beneficiaries may qualify for a program called Extra Help (also known as the Low-Income Subsidy) that covers most or all of the plan’s premiums, deductibles, and copays. For 2026, you may qualify if your annual income is below $23,940 as an individual or $32,460 as a married couple, and your countable resources (savings, investments, and real estate other than your home) are below $18,090 for an individual or $36,100 for a couple.
People who qualify for both Medicare and Medicaid, known as “dual eligibles,” are automatically enrolled in a Part D plan by Medicare. You don’t need to apply or choose a plan yourself, though you can switch to a different one if you prefer. If you receive Supplemental Security Income (SSI), you’re also automatically eligible for Extra Help without filing a separate application.
The $2,000 Out-of-Pocket Cap
Starting in 2025, the Inflation Reduction Act introduced an annual $2,000 cap on out-of-pocket spending for Part D prescription drugs. Before this change, beneficiaries who took expensive medications could face thousands of dollars in costs each year even with Part D coverage. The new cap means that once you’ve spent $2,000 out of pocket in a calendar year, your plan covers the remaining costs. This applies to all Part D plans and doesn’t change who qualifies, but it significantly changes how much Part D is worth to people who take costly medications.
Employer and Retiree Coverage Considerations
If you’re still working and have drug coverage through your employer or union, you may not need to enroll in Part D right away. The key factor is whether your current plan provides creditable coverage. Your plan administrator must send you a notice each year, usually before Medicare’s open enrollment begins in October, telling you whether the coverage meets that standard.
If your employer plan is creditable, you can safely delay Part D enrollment without a penalty. Once that coverage ends (through retirement, job loss, or your employer dropping the benefit), you’ll get a Special Enrollment Period to join a Part D plan. If your employer plan is not creditable and you delay, you’ll face the late enrollment penalty when you eventually sign up. Keeping that annual notice from your employer is worth the effort, because it’s your proof that you had qualifying coverage if Medicare ever questions your penalty-free enrollment.