Mutual Fund performance may not be the most important thing to worry about for investors who want their retirement savings to grow, The Wall Street Journal reports.

While it may seem self-evident, an increase in contributions is the most notable way to help boost long-term returns, according to a new study by Putnam Investments.

The study found that people can build more simply by saving more, not by picking the best funds. That seems simple, but David Tyrie, director of retirement services at Putnam, said that people often fail to heed the basic advice, instead focusing on whether they are in the best-performing funds.

"The big surprise was how little of an impact" improvement in fund investing made over a 15-year period, Tyrie said.

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