) -- It's not exactly a secret Americans are coming up short when it comes to retirement savings.

But until now economists really couldn't put a hard and fast number on the financial challenges Americans faced.

A study provides some clarity. U.S. retirees,

HSBC Group (HBC) reports

, are looking at seven full years of low or no income in retirement.

Some are getting the idea. A

separate study from Ally Bank

says 37% of retirees fear they "won't live comfortably" during their golden years.

In the HSBC study,

The Future Of Retirement: A New Reality

, researchers say Americans are looking at a "significant fall in their living standards" in their last seven years of retirement, thanks to retirees doing a lousy job with long-term savings.

Retirees in most countries have the same problem, HSBC says.

"The concept of retirement is evolving all the time, and we knew that the U.S. and the rest of the world is not prepared -- but now we know by just how much," says Andrew Ireland, a senior vice president at HSBC. "People are living longer, through tougher economic times, but expectations about their standard of living in retirement remain unchanged. As a result, millions of people around the world are facing years of hardship after their savings run out."

In the U.S., HSBC analysts estimate that seniors will run out of money 14 years into retirement; on average, Americans spend 21 years in retirement. Thus the seven-year gap.

Internationally, the average timetable for retirement is 18 years, with the average retiree's savings lasting only 10 years. HSBC says that 56% of the global population isn't saving enough for retirement, and almost 20% haven't saved anything for their golden years.

The falls squarely on retirees, the study notes, as 43% of adults across the globe place a larger priority on going on vacation than saving for retirement. Another 29% say they "raided" their retirement savings to buy a new home or pay for their child's college tuition.

"People throughout history have faced the question of how to provide for the future, and today's savers are no exception," Ireland says. "Yet as daunting as the current challenges may seem, the solution is very simple: The earlier you start to plan, the better prepared you will be."

There seems to be two choices to close that retirement savings gap.

"For some this may mean beginning to save more, whereas others will choose to work longer. The key is for everyone, regardless of age or income, to make a plan to help them get the retirement they expect."