Odds Are You're Wrong About This Basic Social Security Rule

Social Security is probably going to be a very important source of income for you during your later years. It cannot be your only income source, as you'll need money in retirement plans to supplement it. Still, your benefits will almost definitely help you to pay your bills as a senior once your paychecks stop.

Unfortunately, even though many retirees rely on Social Security, many Americans don't understand even one of the most basic rules about how the benefits program works. Worse, it's not just that Americans don't understand. The majority are wrong about a rule in a way that could cost them many thousands of dollars over their lifetimes.

Here's the Social Security rule that most people are incorrect about, so you can see if you're also making a fundamental mistake when it comes to your retirement benefits.

Image source: Getty Images.

Most Americans get this critical Social Security rule wrong

The basic Social Security rule that most people get wrong has to do with full retirement age (FRA). This is the age you must reach in order to be eligible to claim a standard unreduced benefit. And odds are, you are wrong about when that age is.

That's because, as a new survey from Allianz Life Insurance Company of North America revealed, 55% of Americans believe that the full retirement age for Social Security is 65. This is simply not true, and it has not been for a long time.

The reality is that FRA varies depending on your birth year. Here's what your full retirement age is, based on the age when you were born:

• 1943 to 1954: 66
• 1955: 66 and two months
• 1956: 66 and four months
• 1957: 66 and six months
• 1958: 66 and eight months
• 1959: 66 and 10 months
• 1960 or after: 67

If you are assuming that your FRA is 65, as most people do, you could end up shrinking your benefits by a substantial amount as a result of this mistaken belief.

Why do so many Americans get FRA wrong -- and what does it mean for them?

So, why are Americans so confused about when FRA is for Social Security? The reality is, it's easy to make this retirement planning mistake, because the FRA was 65 when the Social Security benefits program was originally created. It was gradually moved later as a result of reforms in the 1980s that were necessary because Social Security was running short of money.

Since a lot of people aren't that familiar with 1980s law changes, and since the latter FRA was phased in slowly, many future retirees just don't realize that 65 isn't the critical age anymore. And, of course, it doesn't help that Medicare eligibility still begins at 65. It's natural to assume that once you become eligible for Medicare, you'll also be eligible for your full Social Security benefit.

The problem is, this misconception has consequences. Every month you claim Social Security before your FRA results in a reduction in benefits. You become eligible to start checks at 62, so if you think your FRA is 65, you may underestimate how much an early claim will shrink your payments.

Or, you may wait until 65, claim your benefit, and not even realize you're getting hit with two years of early filing penalties and shrinking your benefits by around 13.3%. This is a big problem, since Social Security benefits are protected against inflation and guaranteed to last for life -- and shrinking them without knowing it can reduce the income available from this important source.

It's critical you don't make this mistake and end up unexpectedly having to rely more on your 401(k) or other investments than you planned because you've shrunk your Social Security payments for life. Find out what your actual FRA is based on when you were born, and make a fully informed claiming choice with this correct information in mind.

The Motley Fool has a disclosure policy.