Medicare eligibility age: when you can enroll and what happens if you wait

If you collect Social Security retirement or Railroad Retirement Board benefits at least four months before your 65th birthday, you are enrolled in Medicare Part A (hospital insurance) and Part B (medical insurance) automatically. Your card arrives in the mail before your coverage start date.

If you are not yet collecting Social Security at 65, you need to enroll yourself. This is common for people who delayed Social Security to earn a larger monthly benefit.

The Initial Enrollment Period (IEP) is the first opportunity most people have to sign up for Medicare. It runs for seven months: the three months before your birthday month, your birthday month itself, and the three months after. For example, if your birthday is in June, your IEP runs from March through September.

When you enroll matters inside that window. Signing up in the three months before your birthday month means coverage starts on the first day of your birthday month. Waiting until your birthday month or later pushes the start date back by one to three months. Earlier is generally better if you want seamless coverage.

The IEP also applies to Part D (prescription drug coverage) and Medicare Advantage (Part C), the private-plan alternative to Original Medicare that combines Part A, Part B, and usually Part D.

Missing the IEP without a qualifying reason leads to two separate problems: a gap in coverage and permanent premium penalties.

Part B late-enrollment penalty. The Part B penalty adds 10% to your monthly premium for each full 12-month period you were eligible but did not enroll. It is permanent. In 2026, the standard Part B premium is $202.90 per month. A two-year delay with no qualifying coverage would add 20% to that base for life.

Part D late-enrollment penalty. The Part D penalty applies when you go 63 or more consecutive days without creditable drug coverage (coverage at least as good as standard Medicare Part D) after your IEP ends. The penalty equals 1% of the national base beneficiary premium for each full month you lacked coverage. The 2026 national base beneficiary premium is $38.99. Like the Part B penalty, it is permanent and added to your monthly premium.

The working exception: special enrollment periods

If you or your spouse is actively working and covered by an employer group health plan at a company with 20 or more employees, you qualify for a Special Enrollment Period (SEP). You can delay Part B and Part D without penalty while that employer coverage is active. Once employment or the employer coverage ends, whichever comes first, an eight-month SEP opens for Part B. A separate SEP applies for Part D.

Two critical cautions here. First, COBRA continuation coverage and retiree coverage do not count as active employer coverage for SEP purposes. Relying on COBRA after leaving a job means your SEP clock is already running. Second, if your employer has fewer than 20 employees, Medicare pays primary and delaying Part B can leave you with real coverage gaps.

If you have been contributing to a Health Savings Account (HSA), enrolling in any part of Medicare, including premium-free Part A, ends your eligibility to make new HSA contributions. Part A can backdate up to six months, so it is worth timing your Medicare enrollment carefully if HSA contributions matter to you.

Age 65 is not the only path to Medicare.

Social Security Disability Insurance (SSDI). People who receive SSDI benefits become eligible for Medicare after 24 months of receiving those benefits. The two-year clock begins with the first month of SSDI entitlement, not the application date.

ALS (amyotrophic lateral sclerosis). Medicare coverage begins the same month SSDI benefits start, with no waiting period.

End-stage renal disease (ESRD). People with permanent kidney failure requiring dialysis or a transplant can enroll in Medicare at any age. The timing depends on when dialysis begins or when a transplant takes place.

Understanding the age of eligibility also means knowing what Medicare costs at enrollment.

Part A is premium-free for people with 40 or more quarters, roughly 10 years, of Medicare-taxed work. If you have 30 to 39 quarters, the 2026 Part A buy-in premium is $311 per month. Fewer than 30 quarters means the 2026 full buy-in premium is $565 per month.

In 2026, the annual Part B deductible is $283. After that deductible, Medicare pays 80% of approved costs and you pay the remaining 20%, with no annual cap on that 20% under Original Medicare. Medigap (Medicare Supplement Insurance) policies can cover that 20% exposure, and the best time to buy one is during the guaranteed-issue Medigap open enrollment period, which runs for six months starting the month you are both 65 and enrolled in Part B.

Higher-income enrollees also pay Income-Related Monthly Adjustment Amounts (IRMAA) on top of standard premiums. IRMAA surcharges begin for individuals with modified adjusted gross income above $109,000 (or $218,000 for joint filers), based on income from two years prior. Higher earners pay more through additional tiers for both Part B and Part D. If your income has dropped significantly since that reference year, you can request a new determination using IRS Form SSA-44.

To find out more about coverage options that fit your situation, please contact us to discuss plan options.