Image: Mature couple calculating expenses © Abel Mitja Varela, the Agency Collection, Getty Images

"You'll regret it. Maybe not today, maybe not tomorrow, but soon, and for the rest of your life."

Those words, spoken on a tarmac at the finale of the classic film "Casablanca," could be stretched from the intended affairs of the heart to how we plan for retirement.

There are financial decisions we make that seem a good idea at the time, retirement moves we make halfheartedly and needed plans we sweep under the carpet. When it comes to ensuring a lifetime of retirement income, bad decisions may not hurt immediately, but once the pain arrives it can last for decades.

Here are five retirement mistakes that will haunt you, and ways to avoid the haunting entirely:

1. Guesswork, not legwork

How much will you need to retire?

That straightforward question should be a starting point for people of all ages, at all stages of planning. A great number of people, however, do no more than guess at what they should save.

According to the Transamerica Center for Retirement Studies, a nonprofit organization funded by Transamerica Life Insurance, half of workers continue to guess at the amount of money they need to save to feel financially secure when they retire, and a large number (44%) of American workers do not have a strategy to reach their retirement goals.

Of those who do have a strategy, only half have factored in health care costs and one-fifth have factored in long-term care insurance, so their estimates can be inadequate. A reduction or loss of Social Security benefits ranks third in greatest retirement fears.

As part of its research, Allianz Life asked a segment of baby boomers how much money they thought they would need to live on.

"The average number they came up with was $60,000," says Katie Libbe, vice president of Consumer Insights for Allianz Life. "Then we asked them to try to calculate what that means in terms of a portfolio that's going to deliver that for as long as they think they are going to be in retirement. They were at a loss in terms of what they would need.

"They said $500,000 when, if you just apply a 4% withdrawal to that portfolio, they would really need $1.5 million," Libbe said. "They don't know how to do even this basic calculation. You can teach them about some of these individual tactical mistakes, but they can be off even in the strategic sense of how much money needs to be socked away."

Not only is there the danger of not ensuring the longevity of your savings; there is also the temptation of being unreasonably aggressive with your portfolio to make up for not saving as much as you should have. (Are you saving enough for retirement? Use this MSN Money calculator to find out.)

Health care costs also need to be considered. According to research by Allianz Life, the average couple retiring at age 65 will spend approximately $285,000 in health care costs in retirement. As life expectancies continue to increase, baby boomers need to have a plan for covering some portion of managed care for an elderly parent as well as for themselves.

Health care costs, Libbe says, could "eat into a good chunk of their nondiscretionary dollars, which means fewer dollars available for all the fun things they want to do in retirement."

2. 'I'll just keep working'

Most people assume they will retire at a certain age, and many look to salvage inadequate savings by working later into life.

But according to Limra, a global association of insurance and financial services companies, two in five people retire earlier than planned due to a number of factors, including layoffs or illness. For those assuming they will work part time in retirement, many can't due to circumstances beyond their control.

"We did some research recently where we found out that a lot more baby boomers are planning to work longer," Libbe says. "That's basically their backup plan for not having saved enough for retirement. The Limra statistic about two in five people retiring earlier than they expected just shows you can't count on working longer being your plan."

Making the prospect of retiring ahead of schedule all the more precarious is that 70% of respondents to the Transamerica Center survey agreed they could work until age 65 and still not have enough money saved to meet their retirement needs.

"Planning not to retire is simply not a viable retirement strategy," says Catherine Collinson, the president of the center. "Planning to work past age 65 is an important opportunity to continue earning income, save more and help to alleviate a retirement savings shortfall. However, it's important that workers be proactive in setting a retirement savings goal, saving and investing for retirement and having a backup plan if they are forced to retire sooner than expected."

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3. Taking a loan against your 401k

Close to one in 10 workers with qualified retirement plans from their employers took out a loan in the 12 months leading up to its study, according to the Transamerica Center.

The center's 12th Annual Transamerica Retirement Survey, conducted among 4,080 U.S. workers, found that the majority of those taking out loans (42%) did so to pay off debt; 14% did so to buy a primary residence. Only 6% did so in response to medical bills, and even fewer (3%) found it necessary for tuition expenses.

Though commonly viewed as "borrowing from yourself," those who fail to repay can be saddled with taxes and penalties. Borrowing against a retirement plan also reduces the ability of those funds to earn interest, a loss that will compound in perpetuity. (Will your 401k provide enough income? Find out with MSN Money's calculator.)

4. Not taking full advantage of benefits

Leaving money on the table will hurt you later in life.

According to the independent investment adviser Financial Engines, the recession hurt participant savings rates, with 39% of participants not saving enough to get their full employer match, up from 33% in 2008. Of participants under age 40, 47% failed to save enough to get the full employer match.

In tight economic times, it is understandable that households need to cut costs in many ways. But every dollar not added to your portfolio will miss out on the matching company funds and compound interest that can accrue for years to come.

5. Not having a tax strategy

Many fail to consider the tax impact when withdrawing from their nest egg, Libbe says.

When in retirement, the objective changes from accumulation to converting investments into "tax-smart" income. A tax-efficient withdrawal plan can make a significant difference in how long your portfolio lasts. Retirees need to optimize taxable and tax-advantaged accounts to minimize tax-bracket impact, as well as other income such as Social Security.

"You can actually make your retirement assets last longer if you know how to take distributions from them in retirement so that you are efficient with your taxes," Libbe says. "It is not easy for the average consumer to do, but there are financial advisers and software programs who can do exactly that. They can make sure you don't bump up into a new tax bracket and you are paying attention to required minimum distributions. It can be as simple or complex as you want to make it."

Avoiding the pitfalls

The Transamerica Center for Retirement Studies recommends seven steps to help avoid these and other retirement mistakes that can have a lifelong impact:

  • Get the conversation going with friends and family. Just 9% of workers frequently discuss saving, investing and planning for retirement with family and friends.
  • Formulate a plan and write it down. Only 10% of workers have written out their retirement strategy.
  • Get educated. The majority of workers (71%) say they don't know as much as they should about retirement investing.
  • Consider retirement benefits as part of your total compensation. Fifty-three percent of workers would select a job offer with a higher than expected salary but poor retirement benefits over one with excellent retirement benefits and a comparatively low salary.
  • If your employer offers a plan, participate. And if your employer doesn't offer a plan, ask for one. Just 71% of workers report being offered an employee-funded plan at work, while 92% say a plan is an important benefit. However, almost one-quarter of workers (22%) who are offered a plan at work do not participate.
  • Make catch-up contributions. Just over half of workers (56%) are aware that people age 50 and older are allowed to make catch-up contributions to their retirement plan.
  • Have a backup plan in the event you are unable to work before your planned retirement. Only 19% of workers have a backup plan.

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