En español | There are two main categories for qualifying for Medicare: You can become eligible at age 65 or older or at an earlier age due to disability. But in each case you must meet certain conditions:
Qualifying on the basis of age:
You must be 65 or older and
To be “fully insured” you must have earned at least 40 work credits through paying Medicare payroll taxes at work (equivalent to about 10 years of employment). This guarantees that you pay no monthly premiums for Part A hospital insurance. You can also qualify for premium-free Part A on the work record of your spouse, including (in some circumstances) a divorced or deceased spouse. If neither you nor your spouse has earned 40 work credits, you can nonetheless receive Part A benefits by paying monthly premiums for them.
You don’t need any work credits to qualify for Part B or Part D services — you just pay the required monthly premiums.
Qualifying on the basis of disability
If you’re under age 65 and qualify for Social Security disability benefits, in most circumstances you must wait for two years before qualifying for Medicare. Your Medicare coverage begins during your 25th month of receiving disability benefits. These months need not be consecutive; any time spent receiving Social Security disability counts toward the two-year waiting period.
Two groups of people can receive Medicare sooner:
If you have ESRD, you need to be fully insured or be the spouse or child of someone who is fully insured to qualify for Medicare. (“Fully insured” means having earned 40 work credits through paying Medicare payroll taxes at work.) The start of Medicare coverage depends on what kind of care you need (dialysis or a kidney transplant) and whether you have coverage under an employer plan. For details, see the official publication "Medicare Coverage of Kidney Dialysis & Kidney Transplant Services (PDF)."
If you have ALS, you must apply for Social Security disability. Your Medicare coverage begins at the same time as you start receiving disability benefits (usually five months after your disability application has been approved).