To qualify for Medicare Part B, you need to be 65 or older and either a U.S. citizen or a permanent resident who has lived in the United States for at least five continuous years. You can also qualify under 65 if you have certain disabilities or medical conditions. Beyond age and residency, what you’ll pay depends on your income, and when you sign up matters more than most people realize.
Age and Residency Requirements
The standard path to Medicare Part B is turning 65. If you’re a U.S. citizen, that’s the only demographic box you need to check. If you’re a lawful permanent resident (green card holder), you must have lived continuously in the U.S. for five years before the month you apply. Temporary visa holders and undocumented residents do not qualify.
Part B is optional and separate from Part A (hospital coverage). You aren’t automatically locked into it. But choosing to delay enrollment carries real financial consequences, which we’ll cover below.
Qualifying Under 65 With a Disability
If you receive Social Security Disability Insurance (SSDI), you become eligible for Medicare after 24 consecutive months of receiving those benefits. The clock starts from your first disability payment, not from the date of your diagnosis or application. Once that two-year waiting period passes, you’re automatically enrolled in both Part A and Part B.
There are two exceptions where the 24-month wait doesn’t apply:
- ALS (amyotrophic lateral sclerosis): Medicare coverage begins the same month your SSDI benefits start. There is no waiting period.
- End-stage renal disease (ESRD): You can qualify at any age if your kidneys have permanently failed and you need regular dialysis or a kidney transplant. You or your spouse must have worked enough to qualify for Social Security or Railroad Retirement benefits.
How ESRD Coverage Works
The ESRD path has its own enrollment timeline that differs from standard Medicare. Coverage typically starts on the first day of the fourth month of dialysis treatments. That three-month waiting period runs regardless of whether you’ve formally signed up yet.
You can skip the waiting period entirely if you train for home dialysis at a Medicare-certified facility during your first three months of treatment and your doctor expects you to complete the training. If you’re getting a kidney transplant instead, coverage can begin the month you’re admitted to a Medicare-certified hospital for the procedure, as long as the transplant happens within two months of admission.
One detail that catches people off guard: if you already have employer or union health insurance when you become eligible through ESRD, your group plan remains the primary payer for a 30-month coordination period. Medicare pays second during that window. A new 30-month period starts each time you enroll in Medicare based on kidney failure.
If you’re eligible for Medicare through ESRD but don’t sign up right away, your coverage can be applied retroactively up to 12 months before the month you apply.
What Part B Costs in 2025
The standard monthly premium for Part B in 2025 is $185.00. Most people pay this amount, which is typically deducted directly from their Social Security check. The annual deductible is $257, meaning you pay that amount out of pocket before Part B starts covering its share of costs. After the deductible, Part B generally covers 80% of approved services.
Higher earners pay more. Medicare uses a system called the Income-Related Monthly Adjustment Amount (IRMAA) that adds surcharges based on your tax return from two years prior. For 2025 premiums, Social Security looks at your 2023 modified adjusted gross income. If you filed as single and earned more than $106,000, or filed jointly and earned more than $212,000, your premium increases on a sliding scale. The surcharges rise through several income tiers, with the highest earners paying roughly three and a half times the standard premium.
When to Sign Up
Your Initial Enrollment Period is a seven-month window centered on the month you turn 65. It opens three months before your birthday month, includes your birthday month, and closes three months after. If you sign up during the three months before you turn 65, your coverage starts on the first day of your birthday month. Signing up later in the window delays your start date by one to three months.
If you have health insurance through your own or a spouse’s current employer, you generally don’t need to enroll at 65. You get a Special Enrollment Period that lets you sign up penalty-free within eight months of leaving that job or losing that coverage, whichever comes first. COBRA and retiree health plans do not count as current employer coverage for this purpose.
The Cost of Waiting Too Long
Missing your enrollment window without qualifying for a Special Enrollment Period triggers a late enrollment penalty that, for most people, lasts the rest of their lives. The penalty adds 10% to your monthly premium for every full 12-month period you could have had Part B but didn’t. If you delayed two years, for example, you’d pay 20% more on top of the standard premium every month for as long as you have Part B.
You’d also have to wait for the General Enrollment Period, which runs from January 1 through March 31 each year, with coverage not starting until July 1. That gap means months without coverage on top of the permanent penalty. For someone paying the 2025 standard premium of $185, a two-year delay would add $37 per month indefinitely.