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.

Franklin Small Cap Growth R6 (FSMLX Quick QuoteFSMLX - Free Report) : 0.67% expense ratio and 0.62% management fee. FSMLX is one of many Small Cap Growth mutual funds; these funds tend to create their portfolios around stocks with market capitalization of less than $2 billion. With annual returns of 8.55% over the last five years, this fund is a winner.

T. Rowe Price Institutional Small-Cap Stock (TRSSX Quick QuoteTRSSX - Free Report) : 0.66% expense ratio and 0.65% management fee. TRSSX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. TRSSX, with annual returns of 9.22% over the last five years, is a well-diversified fund with a long track record of success.

John Hancock Disciplined Value R6 (JDVWX Quick QuoteJDVWX - Free Report) is an attractive large-cap allocation. JDVWX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. JDVWX has an expense ratio of 0.65%, management fee of 0.61%, and annual returns of 10.7% over the past five years.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.