Medicare has four parts: Part A for hospital care, Part B for outpatient and physician services, Part C (Medicare Advantage) for plans from private insurers, and Part D for prescription drugs. Each has its own costs, rules, and enrollment timing.
If you do not sign up for Part B when first eligible and have no Special Enrollment Period, your premium rises 10% for each full 12 months you could have had it, usually for as long as you have Part B.
It depends on employer size. If your (or your spouse’s) employer has 20+ employees, that plan usually pays first and you can delay Part B without penalty. If the employer has fewer than 20 employees, Medicare typically pays first, so you generally should enroll in Part B at 65.
When you retire, your active employer coverage usually ends, which triggers an 8-month Special Enrollment Period to sign up for Medicare Part B without penalty. Some employers offer retiree coverage or an HRA that works alongside Medicare.
Part A covers hospital/inpatient care, Part B covers doctors and outpatient care, Part C (Medicare Advantage) is a private all-in-one alternative to A and B, and Part D covers prescription drugs.
Your first chance is the 7-month Initial Enrollment Period around your 65th birthday. After that, the Annual Enrollment Period (Oct 15 to Dec 7) lets you change Medicare Advantage and Part D plans, and Special Enrollment Periods apply after events like leaving employer coverage.