You have a small window in which to sign up for Medicare. Perhaps the most compelling reason to retire at age 65 is Medicare eligibility. Once you turn 65 you no longer need to hold on to a job for the health insurance coverage. You can sign up for Medicare beginning three months before your 65th birthday and start coverage the month you turn 65. It's important to sign up during the seven-month window around your 65th birthday, because your Medicare Part B and D premiums can be increased if you enroll later. Beginning the month you turn 65 there is also a six-month Medigap enrollment period during which you can buy any Medigap policy sold in your state. If you don't sign up then you could potentially be charged significantly higher premiums or even denied coverage. If you are still working at age 65 and have a group health plan through your or a spouse's job, you should sign up for Medicare within eight months of leaving the position or health plan to avoid the higher premiums.