Mistake No. 4: Leaving the account in limbo

Just leaving your retirement account with a former employer is also a bad option, Hottin says.

"If your former company downsizes or is acquired by another firm," he says, "finding some contact who can help you retrieve it at a later time could be a hassle.

"It's better to take your 401k with you and mix it in with your new employer's plan -- or roll it into an individual retirement account of some type so you can manage it a bit better." If you do an IRA rollover, make sure it's a trustee-to-trustee transfer.

Rolling it into your new employer's account will give you continued creditor protection, says Green. "Even if you default on loans or you're a defendant in a lawsuit and lose, nobody can touch the money in your 401k or 403b." Depending on the state you live in, he says, your money might also be protected in an IRA.

Mistake No. 5: Too much company stock

Financial advisers say you should have no more than 10% of your retirement account in your employer's company stock. If you're concentrated in a single security, you get hit with a double whammy if your company hits hard times and you lose your job.

"Having company stock in a 401k plan is good for the company in a few ways, but it's a bad idea for the nonowner employees in many ways," Gordon says. "If you're thinking, 'What about the Facebook or Google employees who are now millionaires because of their stock?' don't confuse luck with skill. On the streets of this nation, there are many former employees of Enron, PanAm, WorldCom and others who also believed in their company's stock."

Sometimes, companies make their stock available to employees at a discount through stock options or other direct-purchase programs, he says. If you're tempted, "you are probably best served by taking advantage of the discount and realizing the gain on the discount as soon as (feasible)."

Mistake No. 6: Ignoring the big picture

Your employer-sponsored retirement plan is just one leg of the proverbial three-legged stool of a retirement plan.

"One of the largest mistakes is lack of planning in a holistic sense," Hottin says. "People fail to consider their retirement plans as part of the bigger picture. Your employee retirement account should be part of an overall strategy of financial well-being."

In other words, Green says, the term "retirement plan" should refer not just to tax-qualified plans such as IRAs and 401k's, but also other sources of income such as Social Security, company pensions, part-time work and other money saved up -- "your overall plan for how you're going to get through the remainder of your life."

Of course, many variables are beyond your control: You don't know how long you will live, how your investments will perform or whether you'll encounter an unforeseen expense that could derail your plans. So the best way to plan for the unexpected is to spend less, invest as much as you can and choose investments wisely.

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