Millions of seniors today get health coverage through Medicare. If your 65th birthday is approaching, it may be time to sign up for Medicare. The good news is that you don't need to drag yourself out to a Social Security office to do so -- you can painlessly complete the process online.

When to enroll in Medicare

Medicare eligibility begins once you turn 65, but you actually get a seven-month initial enrollment window to register. That period begins three months before the month of your 65th birthday, and it ends three months after the month you turn 65. It pays to sign up for Medicare on time, because if you don't, you'll risk a lifelong surcharge on your Part B premiums.

Older woman typing on laptop; next to laptop are a mug and book

IMAGE SOURCE: GETTY IMAGES.

That said, if you're still working at age 65 and have coverage under a group health plan, or have coverage under a spouse's group health plan, then you don't necessarily need to rush to sign up for Medicare for fear that you'll incur a Part B penalty for being late. Those covered under group health plans at age 65 get a special enrollment period to sign up for Medicare once their group coverage ends, and only once that period expires do you need to worry about late enrollment penalties.

On the other hand, it often pays to enroll in Medicare Part A at 65 even if you're covered by a group health plan. The reason? Part A is free for most enrollees, and if you have health insurance through a job, Medicare can serve as secondary insurance and perhaps pick up certain costs your primary plan won't cover. The main reason it wouldn't make sense to enroll in Part A while also covered through work is if you're contributing to a health savings account, since you can't participate in one of those while on Medicare.

Enrolling in Medicare online

Once you make the decision to enroll in Medicare, you have three choices: You can do so in person, over the phone, or online. The latter, however, is usually the quickest way to complete your enrollment.

To enroll in Medicare online, you'll need to create an account on the Social Security Administration's website. Choose a user name and password you'll remember so you don't have trouble logging on in the future.

From there, you'll be asked for some basic information like your name, address, phone number, citizenship status, country of birth, and Social Security number. If you're signing up for Part A only because you're covered through a group health plan at work, you'll need to provide the start date of your employment (or spouse's employment) and the date your health coverage began. You'll also be asked to indicate whether your employment or group health coverage has come to an end, but if you're enrolling in Part A alone, chances are, it hasn't.

Additionally, you'll be asked if you wish to sign up for Medicare only, or if you want to start receiving Social Security retirement benefits as well. While you're certainly allowed to file for Social Security at 65 (in fact, you can do so as early as 62), signing up at that point means claiming benefits ahead of full retirement age. That age may be 66, 67, or 66 and a certain number of months, depending on the year you were born. Filing before full retirement age will reduce your monthly benefit payments, and most likely on a lifelong basis, so if you don't need that money right away, you're better off waiting and letting your benefits grow.

You can absolutely sign up for Medicare by itself at 65, whether you're still working or not. If you don't have health coverage through a job or a spouse's job, you'll probably need to enroll in Parts A and B. As mentioned earlier, you'll be charged a premium for Part B, which you'll need to pay directly if you don't sign up for Social Security at the same time. If you do start collecting Social Security in conjunction with Medicare, you can have your Part B premiums deducted from your benefits.

Securing the coverage you need

Enrolling in Medicare online is an easy process that will, in most cases, take 20 minutes or less. If you're creeping toward 65, it pays to look into signing up for Medicare to ensure that you have the health coverage you need, when you need it.