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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

Ivy Large Cap Growth N (ILGRX Quick QuoteILGRX - Free Report) : 0.64% expense ratio and 0.6% management fee. ILGRX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. With annual returns of 14.39% over the last five years, this fund is a winner.

Davenport Small Cap Focus Fund (DSCPX Quick QuoteDSCPX - Free Report) . Expense ratio: 0.89%. Management fee: 0.75%. DSCPX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. This fund has managed to produce a robust 12.1% over the last five years.

Fidelity Mega Cap Stock (FGRTX Quick QuoteFGRTX - Free Report) : 0.62% expense ratio and 0.42% management fee. FGRTX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. With a five-year annual return of 12.25%, this fund is a well-diversified fund with a long track record of success.

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.