Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

Goldman Sachs Large Cap Growth Insights Service Class (GSCLX Quick QuoteGSCLX - Free Report) : 1.06% expense ratio and 0.51% management fee. GSCLX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. GSCLX has achieved five-year annual returns of an astounding 15.96%.

JPMorgan Mid Cap Growth Fund A (OSGIX Quick QuoteOSGIX - Free Report) . Expense ratio: 1.14%. Management fee: 0.65%. OSGIX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. This fund has managed to produce a robust 15.21% over the last five years.

T. Rowe Price Institutional Small-Cap Stock (TRSSX Quick QuoteTRSSX - Free Report) . Expense ratio: 0.66%. Management fee: 0.65%. Five year annual return: 12.01%. TRSSX is a Small Cap Blend mutual fund that usually targets companies with a market capitalization of less than $2 billion.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.