"For working seniors with employer-sponsored plans, it may make sense to delay enrollment in Parts B and D to avoid paying premiums for coverage they don't yet need.... Medicare allows seniors to delay enrollment without penalty if they have coverage through work. But once they retire and coverage ends, they have an eight-month window ... to enroll in Medicare Parts B and D without incurring fines. If they miss that window, they could face late enrollment penalties of up to 10 percent for every year late -- and have to pay higher premiums for the rest of their lives. They could even have to go without insurance while they wait for the next sign-up period."