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.

The easiest way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund Rank of over 19,000 mutual funds, we've identified three outstanding mutual funds that are ideally suited to help long-term investors pursue and achieve their retirement investing goals.

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

If you are looking to diversify your portfolio, consider Deutsche Science and Technology S (KTCSX Quick QuoteKTCSX - Free Report) . KTCSX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. This fund is a winner, boasting an expense ratio of 0.72%, management fee of 0.46%, and a five-year annualized return track record of 21.26%.

Principal Capital Appreciation R1 (PCAMX Quick QuotePCAMX - Free Report) : 1.32% expense ratio and 0.43% management fee. PCAMX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. With yearly returns of 15.38% over the last five years, PCAMX is an effectively diversified fund with a long reputation of solidly positive performance.

John Hancock Disciplined Value R5 (JDVVX Quick QuoteJDVVX - Free Report) : 0.71% expense ratio and 0.61% management fee. JDVVX 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. With a five-year annual return of 13.14%, this fund is a well-diversified fund with a long track record of success.

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.