Aging baby boomers couldn't pick a worse time to retire.

Bond yields and stock dividends are low, pension plans have practically disappeared and home values have yet to fully recover. In addition, medical costs are high and Medicare faces budget cuts.

Yet baby boomers, who save much less than their parents did, have insufficient retirement savings.

Editor's Note: How You Lost $85,000 During the Last Decade. See the Numbers.

"It'll cost more to retire," David Blanchett, head of retirement research for Morningstar Investment Management, told BankRate. "There are certainly more risks facing retirees today than there were for past generations."

Companies have been abandoning pension plans, which guarantee retirees monthly income, in favor of 401(k) plans that put the responsibility of saving and picking investments on employees.

Yet stock and bond investments, according to Research Affiliates, are unlikely to provide the kind of retirement help they did in the past, BankRate reported. In fact, investment returns have been so low in recent years that financial advisors are throwing out previous assumptions for savings.

"A lot of retirees will have significant shocks to their lifestyles when they retire, or sometime after that, because of this savings crisis and funding crisis," Blanchett told BankRate.

Retirees are vulnerable to medical costs that can unexpected wipe out their life savings. Americans are saving less than half as much as in the 1970s and 1980s — only about 4 cents of every dollar of disposable income, BankRate noted, citing data from the Bureau of Economic Analysis.

"We have a baby boom generation that spent almost entirely what they earned during their peak earning years," Chris Brightman, head of investment management at Research Affiliates, told BankRate.

"Now they're looking forward to 30 years of retirement and expecting to earn from their investment portfolio enough to live a similar lifestyle with no drop-off," he said. "But that cannot happen."

Many baby boomers should retire later, experts advise. Hanging on to their current jobs for a few more years is preferable to retiring at 65, and then trying to get back into the work force after running out of money a few years later.

A third of workers ages 55 to 64 have no retirement savings, according to a research by the National Institute on Retirement Security. A third have savings equaling less than one year's salary, far less than what financial planners recommend.

The gap between Americans' retirement savings and what they'll need is estimated at $6.8 trillion, and that's counting their home equity.

Editor's Note: How You Lost $85,000 During the Last Decade. See the Numbers.