The decision to claim Social Security isn't one to take lightly. It's important to put a fair amount of thought into your filing before going through with it.

You're allowed to sign up for Social Security once you turn 62. And there's no financial benefit to delaying your filing beyond age 70. So for the most part, you're looking at an eight-year window in which to sign up.

In the middle of that window is age 65. You may be inclined to claim benefits at that point in conjunction with your Medicare enrollment. But if you go that route, you might regret it after the fact for one big reason.

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Can you afford to slash your benefits for life?

You're entitled to your full monthly Social Security benefit based on your wage history once you reach full retirement age, or FRA. But FRA doesn't kick in at 65.

You might assume that 65 is FRA for Social Security purposes because that's when Medicare eligibility begins. But while the two programs are interrelated, they have separate rules. And as far as Social Security is concerned, you're not eligible for your full monthly benefit until age 66, 67, or 66 and a certain number of months, depending on the year you were born.

Meanwhile, for each month you sign up for Social Security ahead of FRA, your monthly benefit gets reduced. Filing a couple of months early may not result in such a large hit. But if you were born in 1960 or later and have a FRA of 67, then signing up for Social Security at age 65 could mean reducing your benefits substantially.

At that point, you're looking at a roughly 13.34% hit to your monthly retirement income. That's not such a small amount.

You might especially regret signing up for Social Security at age 65 if you don't have a very large retirement nest egg, and your monthly benefits are your main source of senior income. That's why it pays to consider waiting until FRA -- or even beyond -- to file for Social Security.

Don't get confused

If you enroll in Social Security and Medicare at the same time, you'll have your Medicare Part B premium costs deducted from your benefits automatically. That will save you the hassle of having to pay those premiums manually.

But that's not really a reason to claim Social Security up to two years ahead of FRA. Since it's more than possible to sign up only for Medicare at age 65 and wait on Social Security, it pays to consider doing so if you don't have many sources of retirement income at your disposal and expect to rely on your benefits pretty heavily to stay afloat.

Of course, it's easy to see why some seniors might get confused and assume they have to file for Social Security once they're ready for Medicare. After all, Medicare enrollment takes place on the Social Security Administration's website.

But rest assured that you can sign up for only Medicare at the time of your 65th birthday. And waiting to claim Social Security could make for a much smoother retirement, financially speaking.