Beware costly penalties for not enrolling in Medicare on time. iStockphoto By Kimberly Lankford, Contributing Editor May 5, 2017 QI'm going to turn 65 later this year. How far in advance do I need to sign up for Medicare, and when will the coverage actually start?AIf you're already receiving Social Security benefits, you'll automatically be enrolled in Medicare and you'll get your Medicare card in the mail three months before your 65th birthday. Your coverage will start at the beginning of the month you turn age 65 (if your birthday is on the first day of the month, however, your coverage will start on the first day of the month before your birthday). See the Welcome to Medicare booklet for more information. SEE ALSO: 11 Common Medicare Mistakes If you aren't receiving Social Security benefits yet, you'll have to take steps to enroll in Medicare. You can generally apply for Medicare online at the Social Security Administration's website, even if you don't plan to sign up for Social Security for a while. See Medicare Benefits for more information. You have a seven-month window to sign up – starting three months before the month you turn 65 and ending three months after your birthday month (called the "initial enrollment period"). It's a good idea to sign up before your birthday month so you can get coverage as early as possible. If you sign up during the three-month period before your birthday month, your coverage will start on the first day of the month you turn 65 (if your birthday is on the first day of the month, however, your coverage will start the month before you turn 65). If you sign up in the month you turn 65, your coverage will begin on the first day of the next month. If you sign up one month after you turn 65, coverage will begin two months after the month you enroll. And if you sign up two or three months after you turn 65, your coverage will start three months after the month you enroll. Advertisement If you don't sign up within three months after your birthday month, you'll generally have to wait until January 1 through March 31 to sign up, with coverage beginning on July 1 (and you may have to pay a late-enrollment penalty). See Medicare.gov's When Will My Coverage Start? page for more information. If you're still working and have coverage from a current employer, or you're covered by your working spouse's employer, you may not need to sign up for Medicare at 65. You won't have to pay a penalty as long as you enroll within eight months of leaving your job and losing your employer-based coverage. If you work for an employer with fewer than 20 employees, however, you may have to sign up for Medicare at 65, even though you’re still working, because Medicare usually becomes your primary coverage. Even if you're working for a large employer, you may want to sign up for Medicare Part A at 65 because it's usually premium-free (some people choose to delay, however, because you can't contribute to a health savings account after you enroll in Medicare). You may want to wait until you stop working to sign up for Part B, which costs $134 per month for new enrollees in 2017. Part A covers hospitalization; Part B covers outpatient care, such as doctor's services, x-rays and tests. For more information about Medicare, see Medicare FAQs. For details about the sign-up rules and your choices, see When to Sign Up for Medicare –- and When You Might Want to Delay. SEE ALSO: Why Some People Pay Less for Medicare Than Others Got a question? Ask Kim at email@example.com.