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The 401(k) Mistakes That Could Cost You a Bundle

Access to a workplace retirement plan can be a valuable financial perk — if you're using it wisely.
REUTERS/Andrew RC Marshall
REUTERS/Andrew RC Marshall
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Access to a workplace retirement plan can be a valuable financial perk — if you're using it wisely.

Some typical missteps could cost you tens or even hundreds of thousands of dollars over the course of your career.

That's an important consideration, given the shortfall in Americans' retirement savings. In a recent report from insurer Northwestern Mutual, two-thirds of consumers believe there is a chance they will outlive their savings.

Worse yet, a quarter of workers say their family has less than $1,000 in savings and investments, according to the 2016 Retirement Confidence Survey from the Employee Benefit Research Institute and Greenwald & Associates. Only 14 percent said their family has set aside $250,000 or more.

Amping up savings and getting a fuller sense of your retirement needs are key components, but it's also important to have a better understanding of your workplace plan and how to make it work for you, said certified financial planner Harriet J. Brackey, co-chief investment officer of GSK Wealth Advisors in Fort Lauderdale, Florida.

Read More from CNBC: 5 Things You May Not Know About Your 401(k) Plan

"Don't think you have to become a professional money manager to get this right," she said. "It's not rocket science, you can make a good informed decision if you just slow down."

These four mistakes could be costing you money:

Missing the full match

"Not putting in enough to get the company match is the No. 1 mistake people make," said Brackey. Last year, 23 percent of employees didn't get the full match, according to a report from Aon Hewitt.

That's free money you're passing up. A 2014 Fidelity report calculated the average annual employer contribution at $3,540 per employee. Depending on the rate of return and how short you are from a full match, that can add up to more than $100,000 lost over 20 years of working.

Shortchanging your HSA

Tax-advantaged health-savings accounts can help cover current medical expenses, yet workers are missing out on their potential for added retirement savings. Only 38 percent of workers with access to an HSA are contributing to one, and of those, 47 percent are using the money solely to cover short-term expenses, according to an April report from PricewaterhouseCoopers.

Letting HSA assets grow over the long term can be a smart play to cover health costs in retirement — especially for workers in higher tax brackets, said Carolyn McClanahan, a certified financial planner and founder/director of financial planning at Life Planning Partners in Jacksonville, Florida.

Depending on the rate of return, a 2014 report from EBRI found, someone contributing the maximum for 20 years with no withdrawals could expect to amass $118,000 to $193,000.

Cashing out

One in 5 workers empties an old retirement account within five years of leaving a job, according to a 2016 Fidelity analysis. But workers are better off considering other options, said Meghan Murphy, a director at Fidelity Investments — rolling over the funds to their new workplace plan or to an IRA, for example, or even just leaving them be.

Read More from CNBC: Can Your 401(k) Account Be Too Big?

"If you cash out, you've diminished the [compounding] advantage you had," she said.

Fidelity estimated that a 30 year old who cashes out $16,000 from a 401(k) would end up with just $11,200 after taxes and the early withdrawal penalty. Had she let the balance ride, it would have grown to roughly $81,500 by retirement at age 67.

Going all in with a high-fee plan

After you've contributed enough to get the full employee match, consider your options. There are several good reasons — including tax diversity, lower fees and better investment options — that you might want to cut and run, stashing extra retirement savings in other places.

"Some people have just horrible 401(k) plans," said McClanahan. (Check the reviews for yours on

A 2014 Center for American Progress report estimated that over a career, high fees could siphon 20 percent or more from the value of an employee's savings balance at retirement. For a 25-year-old worker starting out with a roughly $30,000 salary, paying 1 percent in fees instead of 0.25 percent meant shelling out $96,027 extra over a lifetime — and working an extra three years to retire with the same account balance as a worker in a lower-fee plan.