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Many Americans believe they will live longer than their parents.

For younger generations, that has led to a big concern: how they will provide financially for those extended years.

That's according to a new online poll from the Longevity Project and Morning Consult, which surveyed 2,200 U.S. adults in December.

Of the individuals polled, 63% said they expect their lives to be longer than their parents'. That rate was even higher for members of Gen Z, those ages 18 to 22, with 70% indicating they expect to live longer.

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Despite those hopes, many individuals are not saving more to prepare for those extended years, the poll found. In fact, many Americans believe they are saving less than previous generations.

In fact, 48% said they are not saving as much for for retirement as they should, and 50% feel unprepared in their ability to plan for their later years.

And many younger Americans feel less comfortable relying on one income source that has been a staple for generations Social Security.

While 83% of baby boomers expect to have some income from Social Security, that drops to 64% for Generation X. Meanwhile, just 42% of millennials and 38% of Gen Z plan to depend on those benefits.

On the other hand, across all generations, Social Security benefits are expected to be one of the biggest sources of income. That's alongside personal savings and investments and 401(k) and 403(b) retirement savings plans.

The results come as Social Security faces a looming funding shortfall. The Social Security Administration's latest estimate projects that the trust funds will be depleted in 2035. At that point, only 80% of promised benefits will be payable, according to the agency's calculations.

"There's probably more irrational worrying than there needs to be," said Sri Reddy, senior vice president of retirement and income solutions at Principal Financial Group.

That's because the system will continue to pay benefits, even if they are reduced, he said.

"It's not like Social Security is going away," he said.

Yet other recent research has shown that living on just Social Security alone in retirement is not enough.

While Social Security helps to shrink the wealth gap between high-wage earners and low-wage earners, many still face poverty in retirement, The New School Schwartz Center for Economic Policy Analysis in New York recently found.

Separately, an analysis by the University of Massachusetts Boston found that there isn't one county in the U.S. where Social Security benefits equal the cost of living. That is, the cost of living is always higher.

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Here's where younger generations expect their retirement income to come from - CNBC