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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

If you are looking to diversify your portfolio, consider Sterling Capital Equity Income I (BEGIX Quick QuoteBEGIX - Free Report) . BEGIX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset. This fund is a winner, boasting an expense ratio of 0.79%, management fee of 0.55%, and a five-year annualized return track record of 11.83%.

Eaton Vance Atlanta Cap Focus Growth I (EILGX Quick QuoteEILGX - Free Report) : 0.78% expense ratio and 0.65% management fee. EILGX 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. EILGX, with annual returns of 15.45% over the last five years, is a well-diversified fund with a long track record of success.

Janus Henderson Global Life Science I (JFNIX Quick QuoteJFNIX - Free Report) : 0.76% expense ratio and 0.64% management fee. JFNIX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy. With a five-year annual return of 11.76%, 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.