Two programs, one agency

Medicare is health insurance; Social Security is income. They are different programs, but the Social Security Administration handles Medicare enrollment and premium collection, which is why they feel connected.

You can claim them at different times. Many people start Medicare at 65 while waiting until full retirement age — or later — to claim Social Security for a larger monthly benefit.

Automatic enrollment

If you are already receiving Social Security benefits at least four months before you turn 65, you are usually enrolled in Medicare Part A and Part B automatically, and your card arrives in the mail. If you are not yet collecting Social Security, you typically need to sign up for Medicare yourself during your Initial Enrollment Period.

Part B premiums come out of your check

If you collect Social Security, your Medicare Part B premium is deducted directly from your monthly benefit. Higher earners may also pay an income-related surcharge known as IRMAA on top of the standard premium.

If you are not yet collecting Social Security, Medicare will bill you directly for Part B instead.

The hold harmless rule and timing

In years when Part B premiums rise faster than the Social Security cost-of-living increase, the "hold harmless" provision protects most people so that their net Social Security payment does not go down. It does not apply to everyone — for example, higher-income enrollees paying IRMAA and some new enrollees.

Because the two benefits are independent, plan them separately: enroll in Medicare on time to avoid penalties, and choose your Social Security start date based on the monthly amount you want.