Emergencies are expensive. That is bad news for many Americans, nearly of third of whom have nothing saved up for a rainy day. 

According to a new financial security index poll from Princeton Survey Research Associates International for Bankrate.com, as many as 66 million adults in the U.S. have exactly zero dollars saved for an emergency — not a single penny. The study found that though personal finance is continuing to steadily improve in recent years, the raw numbers reveal a glaring disparity still exists between many Americans and sound fiscal health. 

"This underscores the fact that it takes time, especially because expenses grow faster than many Americans can save during the home buying, family raising years," Greg McBride, Bankrate.com chief financial analyst, said. “Accumulating emergency savings requires establishing the habit."

For those reasons, millennials, most of whom have not yet taken on the expenses inherent in raising a family or buying a home, fared better than a generation older in the savings department. Only 27 percent of millennials (ages 18-35) reported having nothing saved up for an emergency expense, compared with 33 percent among Generation X adults (ages 36-51). Overall, 27 percent of U.S. adults, as many as 66 million Americans, have nothing saved.

However, even many of those who have saved, have not saved much. Over 18 percent of U.S. adults have only saved enough to cover three months of expenses, while 16 percent have only saved enough for five months. More than half of American adults could not survive for six months were they to lose their jobs or incur some other emergency cost.

The news is not all grim though. The survey, which interviewed 1,000 adults living in the continental United States from June 2 to June 5, reported stronger financial security among American adults for the 25th straight month. 

In general, Americans are feeling upbeat about their personal finances. In May, a survey by the Associated Press and the NORC Center for Public Affairs Research found that nearly two-thirds of Americans were confident in their own financial futures, despite overwhelming anxiety about the U.S. economy as a whole.