Medicare Eligibility: Who Qualifies, When to Enroll, and How to Apply

Medicare is the federal health insurance program that covers more than 67 million Americans — but it is not automatic for everyone, and the rules for who qualifies are more nuanced than most people realize. Age 65 is the headline, but it is far from the only way to become eligible. Disabilities, certain medical conditions, and even your spouse's work history can open the door to coverage.

This guide covers every pathway to Medicare eligibility, explains the enrollment timeline so you do not miss critical deadlines, and walks you through the application process step by step.

Who Is Eligible for Medicare?

Medicare eligibility falls into three main categories. Understanding which pathway applies to you determines when your coverage begins, what you pay, and how you enroll.

• Age-based eligibility: You are 65 or older, a U.S. citizen or qualifying permanent resident, and you or your spouse has a sufficient work history paying Medicare taxes.
• Disability-based eligibility: You are under 65 and have received Social Security Disability Insurance (SSDI) benefits for at least 24 consecutive months.
• Medical condition eligibility: You have been diagnosed with End-Stage Renal Disease (ESRD) or Amyotrophic Lateral Sclerosis (ALS), which triggers eligibility regardless of age.

Age-Based Eligibility

This is the most common path to Medicare. When you turn 65, you become eligible — but eligibility alone does not mean everything is free. Your work history determines what you pay for Part A.

To qualify at 65, you must be a United States citizen or a lawful permanent resident who has lived continuously in the U.S. for at least five years. There is no income test and no health screening.

The critical question is whether you qualify for premium-free Part A, which covers hospital stays, skilled nursing facility care, hospice, and some home health services. To get Part A without a monthly premium, you or your spouse must have worked and paid Medicare taxes for at least 40 quarters — 10 years of work. The Social Security Administration tracks your quarters, and you can check your total at ssa.gov.

The quarters do not need to be consecutive. They accumulate over your entire working life. In 2025, you earn one quarter of coverage for each $1,730 in earnings on which you paid Medicare taxes, up to four quarters per year.

Part B — covering doctor visits, outpatient care, and preventive services — is available to anyone who meets the age and residency requirements regardless of work history. Everyone pays a monthly premium: $185.00 per month in 2025, with higher amounts for people above certain income thresholds.

Disability-Based Eligibility

You do not have to be 65 to get Medicare. If you are under 65 and have a qualifying disability, Medicare coverage is available after a waiting period.

To qualify through disability, you must be receiving Social Security Disability Insurance (SSDI). SSDI has its own five-month waiting period from disability onset before payments begin. Once your SSDI starts, you must wait an additional 24 months before Medicare kicks in — meaning the total gap from disability onset to Medicare eligibility can reach 29 months.

Enrollment is automatic. After 24 months of SSDI, Social Security enrolls you in Parts A and B. Your Medicare card arrives about three months before your coverage start date. You can decline Part B to avoid the premium if you have other qualifying coverage.

Note that SSDI is different from Supplemental Security Income (SSI). SSI is needs-based and typically qualifies recipients for Medicaid, not Medicare. However, some people receive both SSDI and SSI simultaneously, making them dual-eligible for both Medicare and Medicaid.

ESRD and ALS Eligibility

Two medical conditions bypass the normal age and waiting period requirements entirely: End-Stage Renal Disease and Amyotrophic Lateral Sclerosis.

End-Stage Renal Disease (ESRD) is permanent kidney failure requiring regular dialysis or a kidney transplant. You can qualify for Medicare at any age if you have enough work credits for Social Security, are already receiving Social Security or Railroad Retirement benefits, or are the spouse or dependent child of someone who qualifies. Coverage typically begins the fourth month of dialysis, or earlier if you are on home dialysis training or admitted for a transplant.

Amyotrophic Lateral Sclerosis (ALS) — Lou Gehrig's disease — receives the most favorable treatment under Medicare rules. If you are diagnosed with ALS and qualify for SSDI, there is no 24-month waiting period. Medicare begins the same month as your SSDI benefits. Congress created this exception because ALS is rapidly progressive, and the standard two-year wait would be devastating for patients needing immediate care.

Medicare Eligibility for Spouses

You do not need your own work history to qualify for premium-free Part A. The Social Security system allows you to qualify based on a spouse's work record.

Current spouse: If your spouse has 40 or more quarters of work, you can get premium-free Part A at 65 — even if you never worked. Your spouse must be at least 62, and you must have been married for at least one year.

Divorced spouse: If the marriage lasted at least 10 years and you are currently unmarried, you can qualify based on your ex-spouse's work record. Your ex must be at least 62 and eligible for Social Security. Many divorced individuals do not realize this pathway exists.

Widow or widower: Surviving spouses qualify for premium-free Part A based on the deceased spouse's record at age 65. If you remarried after age 60, you can still use the deceased spouse's record. Remarriage before 60 generally disqualifies you unless that subsequent marriage also ended.

Do You Have to Be a U.S. Citizen?

No. Medicare is available to two groups who meet the age or disability criteria:

• U.S. citizens who meet standard eligibility requirements.
• Lawful permanent residents (green card holders) who have lived continuously in the United States for at least five consecutive years before applying.

The five-year residency requirement is strictly enforced. Extended trips abroad could reset the clock. People in the United States without lawful permanent resident status do not qualify, regardless of how long they have lived here or how much they have paid in taxes. Naturalized citizens are fully eligible — the five-year rule applies only to permanent residents who have not yet become citizens.

What If You Don't Have Enough Work Credits?

Not having 40 quarters does not disqualify you from Medicare. It means you pay a premium for Part A instead of getting it free. In 2025, the Part A premium structure is:

• Fewer than 30 quarters: $505 per month.
• 30 to 39 quarters: $278 per month (reduced premium).
• 40 or more quarters: $0 per month (premium-free).

At $505 per month, the full Part A premium adds up to $6,060 per year. If you qualify for Medicaid or a Medicare Savings Program like the Qualified Medicare Beneficiary (QMB) program, your state may pay this premium for you.

Part B has no work history requirement. Anyone who meets the age and residency requirements can enroll by paying the standard $185.00 monthly premium. Before paying the full Part A premium, check whether you qualify through a current or former spouse's work record.

When to Enroll: Initial Enrollment Period

For people qualifying by age, the Initial Enrollment Period (IEP) is a 7-month window centered on your 65th birthday. When you enroll within that window directly affects when your coverage starts.

• Months 1 through 3 (before your birthday month): Coverage starts the first day of your birthday month.
• Month 4 (your birthday month): Coverage starts the following month.
• Month 5 (one month after): Coverage starts two months after enrollment.
• Months 6 and 7 (two and three months after): Coverage starts three months after enrollment.

The earlier you enroll, the sooner coverage starts. Waiting until the final months can create a gap of up to three months with no Medicare. One special rule: if your birthday falls on the first of the month, your entire IEP shifts one month earlier.

What Happens If You're Still Working at 65

If you have employer health insurance at 65, the rules depend on your employer's size.

Employers with 20 or more employees: Your employer plan is primary and Medicare is secondary. You can safely delay Part B without penalty. Most people enroll in premium-free Part A but postpone Part B. When the employer coverage ends, you get an 8-month Special Enrollment Period to sign up for Part B penalty-free.

Employers with fewer than 20 employees: Medicare becomes your primary insurance at 65, even with employer coverage. You must enroll in both Part A and Part B during your IEP. Delaying Part B here results in denied claims from your employer plan and a permanent late enrollment penalty.

Several common situations trip people up. COBRA does not count as current employer coverage — electing COBRA instead of Part B triggers the late penalty. Retiree health benefits from a former employer also do not qualify for a Special Enrollment Period. And if you contribute to a Health Savings Account (HSA), enrolling in any part of Medicare makes you ineligible for new HSA contributions. Since Part A can be backdated up to six months, stop HSA contributions at least six months before enrolling.

Late Enrollment Penalties

Medicare penalties are permanent premium increases designed to discourage people from waiting until they are sick to enroll. They are not one-time fees — they compound over time as base premiums rise.

Part A late enrollment penalty: Applies only to those who pay a Part A premium (fewer than 40 quarters). Your premium increases by 10%, and you pay the higher amount for twice the number of years you delayed. Delay two years, pay the penalty for four years. With the full premium at $505 per month in 2025, that is $50.50 extra per month.

Part B late enrollment penalty: This is the most common and harshest penalty. Your Part B premium increases by 10% for each full 12-month period you could have had Part B but did not — and the penalty is permanent. At the 2025 standard premium of $185.00, a two-year delay adds $37.00 per month ($444 per year) for life. A three-year delay adds $55.50 per month permanently. As the base premium rises each year, the dollar amount of your penalty increases with it.

Part D late enrollment penalty: If you go 63 or more consecutive days without Part D or creditable drug coverage after your initial window, you owe a penalty when you enroll. It is calculated as 1% of the national base beneficiary premium ($36.78 in 2025) times the number of uncovered months — permanent. Going 24 months without drug coverage adds roughly $8.80 per month to your Part D premium for life.

How to Apply for Medicare

How you apply depends on whether you are already receiving Social Security benefits.

Already receiving Social Security retirement benefits: You are enrolled in Parts A and B automatically at 65. Your Medicare card arrives about three months before your birthday. If you do not want Part B, you must actively opt out or premiums will be deducted from your Social Security check.

Already receiving SSDI: You are enrolled automatically after 24 months of SSDI. Your card arrives roughly three months before coverage begins.

Not receiving Social Security benefits: You need to actively sign up. This is common for people still working at 65 or delaying Social Security to increase their monthly benefit. You can apply three ways:

1. Online at ssa.gov — the fastest method. You can apply for Medicare only or for Medicare and Social Security together. It takes about 10 minutes.
2. By phone — call Social Security at 1-800-772-1213 (TTY 1-800-325-0778), Monday through Friday, 8 a.m. to 7 p.m. local time.
3. In person — visit your local Social Security office. Schedule an appointment and bring your birth certificate, Social Security card, and proof of current health insurance.

Once enrolled in Parts A and B, you can choose additional coverage — a Part D drug plan, a Medicare Advantage plan, or a Medigap supplement. Those decisions are made through Medicare.gov or the plans directly, not through Social Security.

The Bottom Line

Medicare eligibility is broader than most people think. You do not have to be 65, you do not have to be a citizen, and you do not have to have 40 quarters of work history — though each factor affects what you pay and when you enroll. The three main pathways are age, disability, and qualifying medical conditions, with spousal benefits and work credit buyins adding important alternatives.

The single most important thing you can do is enroll on time. The Initial Enrollment Period is your best window — signing up during the first three months ensures coverage begins on your birthday month with no gaps and no penalties. If you are still working at 65, understand whether your employer plan is primary or secondary. Getting that wrong leads to denied claims and permanent surcharges.

Part B late enrollment penalties are especially punishing — permanent, percentage-based, and growing each year as premiums increase. A two-year delay may seem minor, but the lifetime cost can reach tens of thousands of dollars.

If you have questions about your eligibility or timing, contact Social Security at 1-800-772-1213, visit ssa.gov, or reach out to your State Health Insurance Assistance Program (SHIP) for free, unbiased counseling. Medicare is one of the most valuable benefits available to Americans — make sure you claim it correctly and on time.