Most workers probably should enroll in Medicare Part A, which is free for most people and covers institutional care in hospitals and skilled nursing facilities, as well as certain care given by home health agencies and care provided in hospices. But ask your employer (or your spouse’s employer, if that’s where you get your coverage) whether your current coverage will change in any way if you enroll in Medicare, even just Part A. Medicare Part B, which covers outpatient and preventative care like doctor visits and tests, has a monthly premium that changes each year (it is $104.90 a month in 2016). Individuals who don't sign up for Part B when they first become eligible can pay a 10 percent premium penalty for each year that enrollment is delayed. However, there is an exception.
Whether you should enroll in Part B while you are still working depends on how many people work for your employer. If your employer has 20 or more employees, you do not need to sign up for Part B right away because your employer's group health plan will be the primary insurer. When you retire, you will have a special enrollment period of eight months to sign up for Part B, without penalty. If your employer has fewer than 20 employees, however, you should enroll in Medicare Part B when you are first eligible. Medicare is the primary insurer, which means it pays before your employer's insurance pays. If you don't enroll, your employer's plan can refuse to cover you for services that Medicare would have covered. That means that you may have to pay for those services out of your own pocket. Before making a decision about Medicare Part B, you should always contact Social Security by dialing(###) ###-####or visiting your local Social Security office.
So to answer your question, you do not have but you need to take in account the requirements outlines in this answer to know if you will be penalized. Since it is free, there is really no reason to delay signing up for part A, but that is up to you.
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