If you aren’t getting benefits from Social Security (or the RRB) at least 4 months before you turn 65, you'll need to sign up with Social Security to get Medicare Parts A and B. However if you are still working and your employer has 20 or more employees, you may be able to delay Medicare Part A and B without having to pay a penalty if you enroll later. If the employer has fewer than 20 employees, you should sign up for Medicare part A and B when your 1st eligible. In this case Medicare pays before your other coverage.
Ask your benefits manager whether you have group health plan coverage (as defined by the IRS). People with group health coverage based on current employment may be able to delay Part A and Part B and won’t have to pay a lifetime late enrollment penalty if they enroll later. If you want to delay both Part A and Part B coverage, you don’t need to do anything when you turn 65.
If you’re eligible for premium-free Part A, you can enroll in Part A at any time after you’re first eligible for Medicare. Your Part A coverage will go back (retroactively) 6 months from when you sign up (but no earlier than the first month you’re eligible for Medicare). If you aren't eligible for premium-free Part A, and you don't buy it when you're first eligible, you may have to pay a penalty.
I am over 65
In most cases, you don't need to do anything until you (or your spouse) retire or you lose the employer coverage. If you didn’t enroll when you were first eligible, the size of the employer determines whether you have to pay a penalty if you enroll later. Learn more about whether you should get Parts A and B and what happens when your employment or coverage ends.
I'm under 65 & Have a Disability
If you are under 65 and collecting Social Security Disability, you will automatically be enrolled into Medicare Part A and B after 24 months. If you are covered under a spouses employer group plan, you maybe able to decline Medicare Part B. You should check with your employer to determine whether you need to keep Medicare Part B.
I have End-Stage Renal Disease (ESRD)
You can get Medicare no matter how old you are if all of these apply:
Your kidneys no longer work
You need regular dialysis or have had a kidney transplant
One of these applies to you:
You've worked the required amount of time under Social Security, the Railroad Retirement Board (RRB), or as a government employee
You’re already getting or are eligible for Social Security or Railroad Retirement benefits
You’re the spouse or dependent child of a person who meets either of the requirements listed above
You automatically get Part A and Part B the month your disability benefits begin.