American workers are throwing away $24 billion each year.

That’s how much is left on the table annually by employees who don’t save enough in their retirement accounts to take advantage of the full employer match, according to estimates from Financial Engines, an investment advisory firm that studied the savings habits of 4.4 million plan participants at 553 companies.

One in four employees missed out on at least part of the match, according to the report. For the average employee, the missed opportunity is equivalent to turning away a check for $1,336 each year.

People who don’t know how much to stash in their retirement accounts are told often by financial advisers to at least save enough in their retirement plans to receive the full company match. Anything less amounts to turning away free money, but figuring out exactly how much should be saved to get the full match will depend on the employer.

Workers should start by understanding how their plan works, says Greg Stein, director of financial technology for Financial Engines. Some companies will match contributions dollar for dollar up to a certain percentage or dollar amount. Other times they match a reduced amount, such as contributing 50 cents for every dollar contributed by the employee.

For instance, someone at a company that will match dollar for dollar for contributions up to 3 percent of pay, and 50 cents after that for contributions up to 6 percent, should contribute at least 6 percent to get the full match.

The share of people missing out on the match generally declines with age, either because retirement is hitting closer to home or because they are making more and can afford it. The portion of people not maximizing the match drops to 16 percent at age 65 from 35 percent at age  25.

The only exception is during the 30s and 40s, when people might reduce their contributions if they’re struggling with child-care costs or education expenses, the report notes.

Of course, some people can’t afford to save enough to get the full match. Low-income workers were more likely to be missing out on the benefit. Some 42 percent of people earning less than $40,000 were not receiving the full match, compared to 10 percent of people earning more than $100,000 a year.

But turning away the cash leads them to miss out not only on the annual match, but on the investment growth those dollars would see over time. The $1,300 annual match would grow to $42,000 over 20 years — not including the worker’s own contributions. For a 25-year-old with 40 years until retirement, it would grow to more than $142,000.

People who can’t save enough now to maximize their match can take small steps to get there, Stein says. Some employees can sign up for auto-escalation, where their contribution rate would be automatically increased by one or two percentage points each year. Workers can also increase their contribution rates every time they get a raise, which would lead to an even bigger payout if it means getting more of the company match.

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