As if the $2 trillion in retirement savings wiped out by the recent troubles in the financial markets wasn't bad enough for older working Americans, Prudential Financial, Inc., is warning them that possible changes in Social Security and higher marginal tax rates may make their personal situations worse.

To help Americans make realistic plans for retirement, Robert Fishbein, a vice president and corporate counsel in Prudential Financial's Tax Department, has offered the final installment in his five-part series of tips on planning for retirement.

"To maximize your retirement income stream and make it last, you need to pay particular attention to the treatment of your Social Security benefit," Fishbein advised. "Specifically, you should know how much of your benefit you'll lose if you're working and how much will be subject to income tax."

For example, Americans who are working in retirement but haven't attained full retirement age-age 66 for those born between 1943 and 1954-may see a reduction in their Social Security benefits. If they are between 62 and 65 in 2009 and make less than $14,160, they won't lose any benefit. However, they'll lose $1 of Social Security benefit for every $2 they make over $14,160. If they turn 66 this year and make more than $37,680, they'll lose $1 of Social Security benefit for every $3 they make over $37,680 prior to the month they reach age 66.

Americans must consider tax implications, too, Fishbein warned. For instance, if an individual is married filing jointly and has income of more than $32,000, half of the individual's Social Security benefit will be subject to income tax. That tax rises to 85 percent of the benefit if the individual's income surpasses $44,000. For single taxpayers, the applicable income numbers are $25,000 and $34,000, respectively.

Fishbein also pointed out that working in retirement could push Americans into a higher tax bracket: their overall income could be greater than in pre-retirement days if they started collecting Social Security and are drawing on other retirement funds too.

"You should consider the impact that working in retirement can have on how you draw down your assets, how long those assets will last, and how this affects your after-tax income stream," Fishbein concluded.