NEW YORK — Good news for investors: We’re keeping more of what’s ours.

Mutual funds charged less to cover operational expenses last year, as a percentage of their total assets.

It was the fourth straight year that the average expense ratio fell for stock mutual funds, according to separate reports from the Investment Company Institute and Morningstar.

Low costs are such a good predictor of success that Russel Kinnel, director of manager research at Morningstar, suggests investors look at a fund’s expense ratio first when considering whether to purchase it.

Stock mutual funds had an average expense ratio of 0.74 percent last year, according to the Investment Company Institute.

That means for every $10,000 in assets, a stock fund took $74 to cover expenses. That’s down from $77 in 2012 and $100 a decade earlier.