Investment advisers say raiding 401(k) can be costly

The number of people participating in 401(k) retirement plans reached an all-time high last year.

Research from Fidelity Investments also reflects a record in average balance: nearly $76,000.

"About 8 percent of their paycheck goes into their 401(k). Many employers match that. So that's an additional 4 percent," said Kathleen Murphy, president of Fidelity Personal Investing.

But another study by online financial advice firm Hellowallet exposes a growing downside.

One in four Americans have raided their 401(k) to pay monthly bills.

Some, whose unemployment is measured in years, not months, say they had no other choice.

Murphy said it can be expensive.

"Because, in addition to taking the money out, you pay tax penalties on that withdrawn money," said Murphy.

Come April 15, those who raided their accounts last year will find out how expensive.

Most personal finance experts say it should be done only as a last resort.

Murphy said this is all the more reason to get an early start at 401(k) contributions.

"The compounding effect of saving when you're in your 20s and the payoff that will have in your 60s when you're ready to retire is phenomenal," Murphy said.

But a phenomenal challenge is getting Americans to stop early withdrawal of about $70 billion from their 401(k)s every year.