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Baby boomers born between 1957 and 1964 held an average of 11 jobs between ages 18 and 46, according to a recent Bureau of Labor Statistics analysis. Job duration increased as these workers aged, but they generally continued to have large numbers of short-term jobs even in middle age. Among jobs started by 40- to 46-year-olds, 33% ended in less than a year, and 69% ended in less than five years.

If you don't consistently save on your own, job-hopping can hinder your ability to retire comfortably. Many 401k plans have vesting schedules and other rules meant to reward long-term employees; those rules often give workers with short tenure little or no benefit. Here are five ways job-hopping can harm your retirement savings:

Leaving before you're vested

Many employers contribute matching funds to employee 401k plans, but workers often don't get to keep that money until they are vested in the plan. Some companies don't fully vest workers in the 401k plan until they have been with the company for as long as five (18%) or six (14%) years, according to a recent analysis of more than 1,700 401k plans administered by Vanguard. Some companies allow workers to keep a gradually increasing percentage of the 401k match based on years of service, while others don't allow workers to keep any of their 401k match until they hit a certain number of years on the job.

"Obviously, if you have an unvested match of any significance, it should be part of the decision-making process," says Jamie Milne, a certified financial planner for Milne Financial Planning in West Danville, Vt. "If you are three days away from it, hang in there for three days. If you are three years away from it, life needs to move on if you don't want to be there."

Surrendering to the urge to cash out

Almost half (45%) of workers who withdrew money from a 401k plan in 2010 failed to roll it over to another retirement account, up from 40% in 2007, according to a Center for Retirement Research at Boston College analysis of the Federal Reserve Board's Survey of Consumer Finances data.

Cashing out a 401k before age 59½.  will cause you to incur significant taxes and fees. For example, a person in the 25% tax bracket who withdraws $5,000 from a 401k will get to keep just $3,250 after paying income tax and a 10% early withdrawal penalty. People who take early withdrawals also miss out on the compound interest they could have accumulated in the time before retirement.

"I know it's tempting, but the most important thing is do not ever withdraw your retirement savings from the account," says Carol Ringrose Alexander, a certified financial planner and the executive vice president of Retirement Investment Advisors in Oklahoma City. "Consolidate your account and move it to an IRA or your new employer if that plan will allow it."

Mismanaging rollovers

Once you decide to move your money, it's important to avoid taxes and penalties while rolling over your money to a new retirement account. It's generally best to have the money transferred directly to the new financial institution. If a check is made out to you, 20% of your account balance will be withheld for income tax. If you don't deposit the full amount, including the withheld 20%, in a new retirement account within 60 days, additional taxes and the early withdrawal penalty may be applied.

"I always recommend that people directly transfer it to an IRA with some very cost-efficient and well-diversified index funds or exchange-traded funds," says Abigail Pons, a certified financial planner for Capella Financial Services in Bangor, Maine. "For people who have several job changes over a career lifetime, it can be very effective to start an IRA and then consolidate every time they leave an employer behind."

If your new employer allows it, you may also be able to transfer the balance to your new 401k plan.

Not saving during enrollment waiting periods

Just over half (59%) of workers are allowed to begin contributing to a 401k plan with their first paycheck. Other workers face waiting periods ranging from three months (17%) to a year (12%) before they become eligible to contribute to a 401k plan, according to a Plan Sponsor Council of America survey.

Most companies also have service requirements before new employees become eligible for a 401k match, often requiring one year (29%) of job tenure before any employer contributions are offered. It's important to find out when you are eligible for both the 401k plan and employer contributions to your retirement account. If there's a long waiting period, it's prudent to do some saving on your own outside the retirement plan.

"I would definitely start an IRA independently, and then there are always taxable options," says Pons. "Max out an IRA first up to the $5,000 limit, and then save into a taxable account."

Not doing the homework on your plan

Once you become eligible for the plan, you need to choose an appropriate savings rate and study your investment options. Many new employees are automatically enrolled in 401k plans, most commonly with the company investing 3% of an employee's paycheck in a target-date fund. However, you should review whether the default savings rate and investment option will meet your retirement income needs. If you aren't automatically enrolled, you'll need take the initiative to sign up.

"People are really busy when they change jobs," says Alexander. "It's hectic, and sometimes you just don't get around to it."

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