Many seniors look to Social Security as a key source of income once they retire. And for some people, those benefits are actually quite generous.

But a few slip-ups on your part could leave you with a lower monthly benefit throughout retirement. Here are a few reasons you might get shortchanged on Social Security.

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1. You didn't work 35 years

Social Security doesn't pay all seniors the same benefit. Rather, the amount of money you'll be entitled to will hinge on what your earnings look like throughout your career.

Specifically, Social Security takes your 35 most profitable years of earnings into account when calculating the monthly benefit you'll be entitled to. But if you don't work a full 35 years, you may not love the benefit you get. That's because for each year you're without an income, you'll have a $0 factored into your benefit calculation.

That's why it's a good idea to try to spend at least 35 years in the labor force. Doing so could also make it easier to build a solid nest egg for retirement, so that's really a win-win.

2. You filed a claim before full retirement age

You're allowed to start collecting Social Security at age 62. But if you file at that age or at any point before full retirement age (FRA), you'll shrink your monthly benefit in the process.

FRA is 66, 67, or somewhere in between, depending on your year of birth. (It's actually a huge misconception that you're eligible for your full benefit at age 65, because while that is when Medicare kicks in, it's not FRA for Social Security purposes). If you file before FRA, your benefit will get reduced on a permanent basis.

The extent of that reduction will hinge on how early you wind up filing. But to give you an example, if your FRA is 67 and you claim Social Security at age 62, you'll shrink your monthly benefit by a whopping 30%. Ouch.

That's why it's so important to know your FRA. You can use this table to see at what age you'll be entitled to your Social Security benefits in full:

Year of Birth

Full Retirement Age

1943-1954

66

1955

66 and 2 months

1956

66 and 4 months

1957

66 and 6 months

1958

66 and 8 months

1959

66 and 10 months

1960 or any time after

67

Data source: Social Security Administration.

3. You never check your earnings statements

There's an easy way to estimate your future Social Security benefit. All you need to do is create an account at SSA.gov and check your yearly earnings statements.

But that's not the only reason it's smart to access those documents. Your earnings statements also contain a summary of your wages. And if your wage information is off, it could lead to a lower benefit in retirement.

Imagine there's a year in which you earned $120,000, only you switched jobs halfway through and somehow, your income from one of those jobs never got reported to the Social Security Administration. In that case, your income may be listed as $60,000 for that year, not $120,000. But since your future monthly benefit is based on your earnings, underreported income could mean getting stuck with less money from Social Security down the line.

That's why not checking your earnings statement yearly could prove to be a costly mistake. A few minutes of your time could help you spot an error, and if you get it corrected, it could spare you from a lower Social Security benefit.

Don't get shortchanged for retirement

No matter what your financial picture looks like going into retirement, it pays to get as much money out of Social Security as you can. Avoiding these blunders could leave you with a more generous benefit to enjoy.