There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

The best way to shortlist great mutual funds is to ensure solid performance, diversification, and low fees. Some are better than others, but utilizing the Zacks Mutual Fund Rank, we have identified three mutual funds that could be solid additions to one's retirement portfolio.

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

American Century Investments Focused Dynamic Growth Investor (ACFOX Quick QuoteACFOX - Free Report) has a 0.86% expense ratio and 0.85% management fee. ACFOX 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 yearly returns of 11.2% over the last five years, this fund clearly wins.

Janus Henderson Global Life Science S (JFNSX Quick QuoteJFNSX - Free Report) : 1.18% expense ratio and 0.64% management fee. JFNSX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy. JFNSX, with annual returns of 9.89% over the last five years, is a well-diversified fund with a long track record of success.

Neuberger Berman Guardian Institutional (NGDLX Quick QuoteNGDLX - Free Report) . Expense ratio: 0.68%. Management fee: 0.63%. Five year annual return: 11.47%. NGDLX 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.

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.