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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