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Just about every week I help someone enroll themselves using the Medicare.gov Plan Finder enroll button up to three months prior to the effective date for IEP, up to two months prior for SEP. Goes through every time. I never call or have client call 800-MEDICAR to enroll so don't know about any restrictions they place on enrollment timing more stringent that the enrollment period rules.The way I understand it is if it's a 10/01 effective date you have to wait until after 09/01 to enroll.