Generally, you are eligible for Medicare if you or your spouse worked for at least 10 years in Medicare-covered employment and you are 65 years old and a citizen or permanent resident of the United States.

If you are not 65, you might also qualify for coverage if you have a disability or with End-Stage Renal Disease (permanent kidney failure requiring dialysis or transplant).

Here are some simple guidelines. You can get Part A at age 65 without having to pay premiums if:

• You already get retirement benefits from Social Security or the Railroad Retirement Board.
• You are eligible to get Social Security or Railroad benefits but have not yet filed for them.
• You or your spouse had Medicare-covered government employment.

If you are under 65, you can get Part A without having to pay premiums if:

• You have received Social Security or Railroad Retirement
• Board disability benefit for 24 months. You are a kidney dialysis or kidney transplant patient.

While you don’t have to pay a premium for Part A if you meet one of those conditions, you must pay for Part B if you want it. It is deducted from your Social Security, Railroad Retirement, or Civil Service Retirement check. If you don’t get any of the above payments, Medicare sends you a bill for your Part B premium every 3 months.

What Isn’t Covered by Original Medicare?

Original Medicare doesn’t cover all of the health care services older people are likely to need in retirement. Original Medicare generally won’t pay for glasses and contact lenses or the routine eye examinations to prescribe corrective lenses. Dental care and hearing aids are also commonly needed services that aren’t covered. Perhaps most significantly, while short-term nursing home stays might be covered under specific circumstances, Original Medicare does not pay for long-term care.

When Should You Enroll in Original Medicare?

Retirees can first enroll in Original Medicare during a seven-month window that begins three months before the month they turn 65. Sign up at the beginning of this period if you want coverage to begin the month you reach age 65. It’s recommended to also sign up for Part D from the start, which helps with prescription drug coverage, even if you don’t take prescription drugs. If you sign up for Part D later, you’ll be required to pay a late enrollment penalty for each year you are enrolled.

If you miss the initial enrollment period, you can sign up between Jan. 1 and March 31 for coverage that will begin July 1, but you will be charged late enrollment penalties for as long as you have Medicare. Late enrollment penalties from Medicare can be long-term, says Anna Maria Chávez, executive vice president and chief growth officer at the National Council on Aging. You don’t want to have to worry about higher costs just because you didn’t act when you became eligible at 65.

If you delay Original Medicare enrollment because you or your spouse is still working at a job with group health insurance, sign up within eight months of leaving the employer or health plan to avoid the penalty.