An overwhelming majority of Americans are heading into retirement without any idea of how much money they will need, according to a new survey.

The personal finance website MoneyRates found in a survey that 71% of adults within 20 years of retirement have not run a projection on how long their savings will last based on their life expectancy.

Moreover, 53% of that group said they expect to retire with less than $100,000 in savings.

The report is the lastest in a series of retirement industry reports that sound a familiar theme: U.S. workers aren't planning for their retirement.

"Saving for retirement is tough enough without approaching it blindfolded," Richard Barrington, MoneyRates' senior financial analyst, and the study's author, said in a statement. "The survey results suggest many people have no clue whether they can afford retirement. How can you hit a target when you don't know what you're aiming at?"

Among those who have reached retirement age, 62% said they didn't know how long their savings should last.

Those nearing or in retirement also were mostly oblivious to how health-care might impact their plans: 71% of pre-retirees and 64% of retirees had not researched the cost of moving into a nursing home or an assisted living facility.

The report also found that 46.8% of respondents age 65 or older reported having less than $100,000 in savings.

Barrington noted that health-care expenses represent 8.1% of consumer spending in general.

"Retirement spending can really escalate if you have to move into an elder care facility," he said, adding that the average annual cost of an assisted living facility as $48,612.

Just over half of all survey respondents expected inflation to increase costs by less than 10% over the next 10 years. But based on the average inflation rate (3.86%) over the past 50 years, prices could increase by 46.11% every 10 years, the report said.

"Even at a more moderate 2% inflation rate, which is the Federal Reserve's target, inflation could increase prices by 21.9% in 10 years," Barrington said. "Lack of budgeting and failing to anticipate the impact of inflation can cause people to spend down their savings too quickly in retirement."

Survey respondents consisted of 500 people between the ages of 45 to 64 and within 20 years of retirement, and a separate group of 500 people ages 65 and older who already reached retirement.