If there's one challenge as daunting as all those years of squirreling money away for retirement, it's this: making sure you don't run out of money during retirement.

You have to figure out how much to withdraw each year. Whether to get a part-time job. Or an annuity. And if you fail to plan for unexpected health care costs, you might have to kiss those exciting travel plans goodbye.

" Fading corporate pensions and longer life spans make it hard to generate enough income to maintain your living standard in retirement — a period that can last nearly as long as your working years. Today, a healthy 65-year-old man can expect to live, on average, 19 more years; an average 65-year-old woman will live close to 22 more years. There's nearly a one-in-three chance that one or both will make it to age 95, says the American Academy of Actuaries.

That's why it’s more important than ever to get professional guidance to know how long you can expect your money to last.

As 79 million baby boomers march into retirement over the next two decades, they risk falling into a trap that Olivia Mitchell, a professor at the Wharton School of the University of Pennsylvania, calls "the lump-sum illusion."

"People look at their 401(k) sum and think, 'I have $100,000 or $1 million; I'm rich,' " Mitchell says. "The danger of the lump-sum illusion is that people don't understand how expensive it is to get old, and they withdraw too much."

Living longer than you expected is preferable, of course, to the alternative. But you can limit the financial risks. Here's how:

•Part-time work.  More retirees are rejoining the workforce, at least part time. In 2005, about 15% of those age 65 and older were in the workforce, compared with nearly 11% two decades earlier, according to government data. A part-time job will fund your daily living expenses in retirement and delay the moment when you have to dip into your principal.

In general, financial planners say you need 65% to 85% of your pre-retirement income after you stop working to maintain the same standard of living. But planners say they're seeing people each year blow through 100% of their pre-retirement income — or more — because they're healthier and more active.

•Government benefits. You can start receiving Social Security payments as early as age 62. But the longer you wait — up until 70 — the higher your payout. That's why planners generally recommend delaying Social Security payments as long as you can. One exception: If you don't expect to live long, because of your health or your family's medical history, consider withdrawing benefits soon after you become eligible, according to Jonathan Guyton, a financial planner in Edina, Minn.

But don't count on Social Security alone to sustain you. These benefits will replace only 40% of yearly pre-retirement income for the average worker, the Social Security Administration says. So you'll likely need other income, too.

If you work while receiving Social Security, your benefits may be lowered until you reach full retirement age, which ranges from 65 to 67 depending on the year you were born. Also be aware: Up to 85% of your Social Security payments could be taxed if you have other income — such as investment earnings — during your payout years.

•Regular withdrawals. To reduce the risk of running out of cash in retirement, you can set up a schedule for withdrawing a stream of income from your portfolio. A rule of thumb is to start at 3% to 4% of your portfolio value and adjust it up each year based on inflation.

If you're willing to monitor your portfolio closely, you can withdraw a far higher rate — 6.2% initially, ramping up each year with inflation — Guyton's research says. "The difference between a 4% and 6% withdrawal for some people could be $1,000 a month," he says. "That extra $1,000 could mean (more) time with your family, traveling, getting season tickets, going to the opera."

If retirees withdraw as much as 6.2% of their account initially, they should follow some guidelines to lessen their risk of running out of money. One guideline: Don't raise your withdrawal rate in years when your portfolio returns turn south.

•Laddering bonds, CDs. Buying bonds or certificates of deposit (CDs) that mature at different intervals gives you a stream of income in retirement while minimizing interest-rate fluctuations.

Suppose you had $50,000. You'd put $10,000 each into five bonds maturing at different times, say in one-, three-, five-, seven- and 10-year bonds. When the one-year bond matures, you'd reinvest the money in a new 10-year bond. You'd do the same as the three- and five-year bonds mature, to build a ladder of bonds that throw off interest at regular intervals.

Bank CDs generally require a lower initial investment than bonds. And up to $100,000 is federally insured. (If you have other accounts at the same bank, $100,000 is usually the maximum insured amount per person across all accounts). On the other hand, certain bonds, such as corporate bonds, tend to offer higher returns than CDs in exchange for greater risk: Your principal isn't guaranteed by the government.

Laddering doesn't guarantee that you won't outlive your money, though. For that, you'll have to turn to your company's pension, if you're lucky enough to have one, or to Social Security or annuities.

•Annuities. Annuities have gotten a bad rap because these insurance products are often highly expensive and complicated. Still, you shouldn't dismiss them outright if you want a guaranteed stream of income.

Some financial planners say retirees should consider putting a portion of their portfolio — say, 25% to 50% — into an income annuity, which pays a stream of income as long as you live. To gauge whether it makes sense, ask yourself whether you have enough steady income to cover your fixed expenses.

Deferred fixed annuities — a cousin to income annuities — also let you take regular withdrawals. But you generally don't do so right away. You can invest the money for decades before converting it into a stream of income. These annuities are a safe and conservative approach to creating an additional guaranteed income stream for life.

•Reverse mortgages. Reverse mortgages are often a last resort for retirees who need income. They let you borrow from your home equity to receive a stream of income for as long as you live in a home. "If I end up living longer than I expected, that's something I can turn to at a later point," says Ken Scholen of the AARP Foundation.

Upfront and monthly fees for reverse mortgages, though, are hefty. The "origination" fee alone typically runs from about $4,000 to $7,000, according to the National Reverse Mortgage Lenders Association. Reverse mortgages usually don't make sense for retirees who plan to move within a few years or who have other income options.

Still, rising home values have made reverse mortgages more appealing because of increased equity available to homeowners.

Matthew Thorp, 85, says he and his wife, Lynn, "fell into retirement" in the early '90s after she became ill and could no longer work. At the time, the couple had $10,000 and a house worth about $500,000.

Their savings weren't enough to pay for the couple's daily living expenses, Lynn's prescriptions and doctors' visits. So the couple took out a reverse mortgage as their Washington, D.C., home climbed in value. They also pawned family heirlooms, furniture and antiques.

Lynn died in 2001. Today, the house the couple bought for $35,000 in the 1960s is worth more than $900,000.

"I'm no role model," Thorp concedes. "I'm just lucky things have worked out. (The reverse mortgage) allowed us to stay here and do things we wouldn't have been able to do otherwise."

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