Social Security provides critical benefits to millions of retired Americans, but if you're worried that the program won't be around for the long haul, you're not alone. In a recent Transamerica study, 77% of workers said they fear the program won't be around once it's their turn to retire. And it's a reasonable concern. Social Security is facing a significant shortfall once its trust funds run out in 2034, at which point incoming taxes will only suffice in maintaining about 79% of scheduled benefits.

So, yes, you should be worried about Social Security -- but not just because of that projected deficit. Rather, what you should be concerned with is the notion of having to live on just 40% of your previous income, because that's all Social Security is designed to replace in a best-case scenario. Furthermore, if benefits are indeed slashed by 21%, you'll get even less replacement income out of Social Security. And that could be disastrous for your retirement.

Worried older man

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You can't live off Social Security, no matter what

Dire as Social Security's impending shortfall might seem, the truth is that Congress still has nearly two decades to step in and come up with a fix. But there's no guarantee that will happen, and even if it does and you get your full benefit payout as scheduled, that income still won't be enough to sustain you in retirement.

Now you may be thinking: "Well, I'll just adopt a frugal lifestyle in retirement and get by on less." It's a good plan in theory, but when you factor in some of the basic expenses functional adults can't live without -- like housing, food, transportation, utilities, clothing, and healthcare -- you'll soon see that living on 40% of your former income just isn't feasible.

In fact, let's talk about healthcare for a minute because it's the one expense that tends to climb in retirement. The average healthy 65-year-old couple today is expected to spend $377,000 on medical care in retirement, and sadly, that figure doesn't even include the cost of long-term care.

Now, according to the U.S. Census Bureau, the average household income in the U.S. was $73,298 in 2014, the last year for which this data is available. Let's say you're nearing retirement and earn roughly that much. Assuming that Social Security will replace 40% of your salary, and that you don't have any additional savings, over the next decade and change, you'll be looking at living on $29,300 a year, or a little more than $2,400 a month. Since, on an individual level, healthcare alone will cost you close to $800 per month based on the above projections, you're looking at just $1,600 to pay your remaining expenses.

And that, of course, assumes that there's no reduction in your Social Security benefits. Come 2034, you might lose 21% of your income, which means you'll be left with just over $1,100 a month to pay your bills once your medical expenses are accounted for.

Even if Social Security is saved, so to speak, it's a bad idea to rely on it as your sole source of retirement income. If you're nearing retirement with that very intention, it's time to change your plans.

There's still time to save

According to the Economic Policy Institute, more than 40% of households approaching retirement have no independent savings to show for. If you're part of that statistic, you should know that you still have an opportunity to amass some savings and help improve your financial outlook.

You can start by maxing out your retirement plan contribution for the current year. Workers 50 and older are allowed to put up to $6,500 a year into an IRA and a generous $24,000 a year into a 401(k).

Once you get into the habit of funding a retirement plan, continue to do so until you've built a reasonable nest egg -- even if that means postponing retirement and working longer than planned. What's a "reasonable" nest egg? That's open to interpretation, of course, but the more money you save, the less likely you are to run into financial trouble during your senior years.

And if you're thinking it's too late to accumulate anything significant in the way of savings, think again. If you have a 401(k) and you max it out for the next five years, you'll have an additional $120,000 to work with in retirement, that doesn't even factor investment growth into the equation.

While you shouldn't have to worry about Social Security going away completely in your lifetime, you should come to terms with the fact that you can't live off your benefits alone. And once you accept that reality, you'll be better positioned to fret less about Social Security and instead focus your efforts on aggressively building your savings.

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