According to a survey by Natixis Global Asset Management (NGAM) this includes 30% of investors with $300,000 to $500,000 of assets, 22% with more than $1 million and 18% of those over age 50.

Many affluent Americans say they can’t afford to save and that they don’t have enough money to set aside savings. Among them are 32% of respondents with less than $1 million in investable assets, 16% of those with more than $1 million in assets and 19% of those over age 50.

One in five respondents (18%) say they would rather spend today than put money away for the future. The survey found 22% with less than $500,000 in assets say they’d rather spend than save, compared with 13% of those with more than $1 million.

“The fact that one in five Americans over age 50 don’t know how much to save is especially troubling, since many Baby Boomers will be retired for decades,” said Tracey Flaherty, senior vice president, retirement strategies, Natixis Global Asset Management. “It’s particularly urgent that these Americans build their savings now, to prepare for secure retirements.”

Steep market movements in the last few years have raised doubt among investors. Overall, 47% say they curbed their savings and investing because they didn’t want to risk losing money.

Few investors surveyed say their portfolios are risky. Concern about market volatility and rising awareness of risk management appears to have had an impact on investors. Only 28% percent of investors rate their portfolios as “risky,” while 47% categorize them as “neutral” and 25% as “not risky.”

Perceptions of risk divided along wealth lines. Just 17% of those with more than $1 million in investable assets label their investment portfolios as “risky,” compared to 33% of those with less than $1 million. More men (35%) than women (19%) classify their investment portfolios as risky, although it is unclear whether this reflects differences in attitudes or actual differences in portfolio risk.

When asked what most motivates them to save, 48% of Americans overall say providing for themselves and their families is their primary objective. Asset growth is the second choice, at 18%, and capital preservation to provide for future generations of their family is third, at 9%. Saving for their children’s education trails at 5%. More women than men (53% compared to 43%) say their top reason to save is to take care of themselves and their families. More men than women (21% compared to 14%) said asset growth is the next biggest motivator for saving.

The Natixis Global Asset Management U.S. Investor Insights Survey was conducted by CoreData Research, which surveyed 463 American adults to better understand their investment attitudes, behavior and sentiments. The survey was conducted in May and July 2011. In addition, NGAM conducted qualitative interviews with investors in October 2011.