Ex post facto laws are specifically banned by the constitution, but a person can get retroactively enrolled in Medicare without worrying about getting punished for it. Normally getting retroactively enrolled in Medicare is a good thing. A person can make previous claims on his new insurance policy that were incurred after the date the federal government determines he is eligible for the program. He also enters an open enrollment period for the prescription drug period. He has 3 months from the date he received the letter to choose to enroll in a prescription drug plan.
Some people who are retroactively enrolled in Medicare receive a check with the mailing. This check does not originate from Medicare, but rather from the Social Security Administration. While the two are mailed together, a person with questions about this particular document needs to contact their local social security office and find out what the reasoning behind it is. Retroactive benefits for a person who receives them because of a disability work the same way for a person who was not enrolled on his 65th birthday. The former situation is far more common than the latter.
Retroactive Medicare benefits also affect a person’s eligibility for Medigap plans. When he receives the notice, he enters the six month open enrollment period on the date he receives the mailing. It does not matter if the six month normal period has already passed. A person who receives the notice gets his open enrollment period just as anyone else. He can select any Medigap plan his provider offers during this period. If he misses the deadline, he must undergo the medical underwriting process, just the same as anyone else.