Medicare provides critical health benefits to countless seniors. You can register for Medicare during the seven-month enrollment period surrounding your 65th birthday, but if you don't enroll on time, you'll face not only a period without coverage, but a penalty that could increase your premiums -- for life. That's why it's important to pay attention to Medicare enrollment deadlines and sign up without delay.

Enrolling in Medicare

Though you're not eligible for Medicare benefits until you turn 65, you can actually enroll in the program beforehand. In fact, your initial enrollment period encompasses a seven-month period that begins three months before the month in which you turn 65 and ends three months after the month in which you turn 65.

Doctor with older patient

IMAGE SOURCE: GETTY IMAGES.

If you fail to sign up for Medicare during your initial enrollment period, you still get more chances to register. Namely, you can sign up during the general enrollment period of January 1 through March 31 of each year. But not signing up during your initial enrollment period could end up costing you.

While most Medicare enrollees don't pay a premium for Part A, which covers hospital visits and the like, they do pay a premium for Part B, which covers preventative care and diagnostic services. This year, the standard Part B premium is $134, though it could be higher or lower depending on your income and whether or not you collect Social Security. If you fail to sign up for Medicare during your initial enrollment period, you'll face a 10% increase in your Part B premium for every 12-month period you were eligible for coverage but didn't enroll. And when you're living on a fixed income, that sort of penalty can really add up over time.

Furthermore, it's not just Part B you have to worry about in terms of late enrollment penalties. If you wait past your first opportunity to sign up for a Part D plan, which covers prescription drugs, you'll face a penalty there as well. This penalty for late Part D enrollment is calculated by taking 1% of the national base beneficiary premium -- which is currently $35.63 -- and multiplying it by the number of months you remain without coverage. That figure then gets rounded to the nearest $0.10 and added to your monthly Part D premium. So, if you go for 23 months without Part D coverage, you'll pay a penalty of $8.20 per month on top of your regular premium. 

Keep in mind that enrolling late won't just subject you to penalties; it also means you'll have a period of time without coverage for medical services or prescription drug needs. And if you encounter a health emergency during that time, the costs might well exceed the penalties you'll pay for late enrollment.

Special enrollment periods

Some seniors are allowed to sign up for Medicare during what's known as a special enrollment period. If this applies to you, you can sign up late without having to worry about paying a penalty. You'll be eligible for a special enrollment period if you're still working during your initial enrollment period and have health coverage under a group plan from your job. Your special enrollment period, which lasts for eight months, will then begin either the month after your employment arrangement ends, or the month after your group health coverage ends -- whichever is first.

Pay attention to deadlines

Because signing up for Medicare late can result in some pretty serious consequences, it's critical that you pay attention to your own personal enrollment deadline. If you're still not sure exactly when to sign up, you can use this handy tool to determine when eligibility kicks in. Then, once you're ready to register, you can enroll online here, directly through the Social Security Administration's website. While you can file for Social Security benefits at the same time as Medicare, you don't have to do so, and since Medicare eligibility kicks in before current workers reach their Social Security full retirement age, it often pays to tackle each enrollment separately.

Finally, don't forget to take advantage of Medicare's services (many of which are free) once you do enroll. The more proactive you are in addressing health issues, the more you'll be able to maximize your benefits over time.