Q. There seem to be different enrollment periods in Medicare. To clear up confusion, can you explain what they are?

A. Yes, different enrollment periods affect people in different circumstances, and it's important to be aware of the ones that apply to you — especially as Medicare has recently changed the dates of some of them and added a new one for 2011 and future years. Here's an explanation of each enrollment period and when to use it:

Initial enrollment period (IEP) for Medicare at age 65

This is the time frame for most people to sign up for Medicare. It runs seven months, starting three months before the month in which you turn 65 and ending three months after that month. (For example, if your birthday is in May, your IEP begins Feb. 1 and ends Aug. 31.)

Use this period to enroll in Part A (hospital insurance) even if you do not intend to enroll in Part B. (An exception may be if you are still working and have employer health coverage that takes the form of a high-deductible plan and a health savings account. See "Can I Have a Health Savings Account as well as Medicare?")

Use this period to enroll in Part B (which covers doctor visits and other outpatient services) if:

• You have no other health insurance.

• You still have health benefits from a former employer but you have retired or stopped working or plan to stop shortly.

• You still have health benefits from the former employer of your spouse who has retired or stopped working or plans to do so shortly.

• You are covered by COBRA insurance that extended employer health benefits after you (or your spouse) stopped working.

• You have group health insurance from an employer with fewer than 20 workers, or your health plan (such as the TriCare program for active or retired military personnel) requires you to enroll in Part B on turning 65.

• You have individual health insurance you have purchased yourself.

• You do not qualify for Part A and have no other health insurance.

• You are living outside the United States.
  

Be aware that if you are in any of the above situations and delay signing up for Part B beyond your IEP you may face a late penalty when you eventually sign up and — perhaps more detrimentally — you will be able to sign up only during the general open enrollment period (see below) at the beginning of each year and coverage will not begin until the following July.

But in other situations, if you continue to work beyond age 65 and have group health insurance from an employer for whom you or your spouse is still working, you may be able to delay signing up for Part B without penalty. See "Special enrollment period for Part B" below.

If you are already receiving Social Security retirement benefits when you turn 65, Social Security will automatically enroll you in Medicare Parts A and B. You have the right to decline Part B within a certain length of time if you or your spouse is still working for an employer that provides your health insurance.

You can also enroll in Part D prescription drug coverage during this initial enrollment period. But if you already have drug coverage from elsewhere — such as a former or current employer, COBRA or the Veterans Affairs health program — you may not need to sign up at this time. See "Special enrollment period for Part D" below.

Initial enrollment period (IEP) for Medicare through disability

If you become eligible for Medicare under age 65 because of disability, you will receive a letter from Social Security saying when your Medicare coverage will begin. It typically starts 24 months after your disability benefits were approved. Social Security will automatically enroll you in Part A and Part B. If you wish to opt out of Part B, you can if you or your spouse is still working for an employer with more than 100 workers that provides health coverage.

When you turn 65, you'll be entitled to a second seven-month IEP — this time based on age instead of disability. You get to start over, so if you previously paid a Part B late penalty, you won't have to pay it any longer.

Special enrollment period (SEP) for Part B

This SEP allows you to enroll in Part B without penalty beyond age 65 provided that you can show you have had group health insurance from an employer (or employers) for whom you or your spouse were still working since you turned 65. The SEP runs for eight months from the date you (or your spouse) stopped working. But you can enroll before this date to ensure unbroken health coverage. Your Part B coverage begins on the first of the month after you enroll.