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, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

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

Hood River Small Cap Growth Institutional (HRSMX Quick QuoteHRSMX - Free Report) : 1.06% expense ratio and 0.9% management fee. HRSMX 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. HRSMX has achieved five-year annual returns of an astounding 12.6%.

Deutsche Science and Technology S (KTCSX Quick QuoteKTCSX - Free Report) : 0.7% expense ratio and 0.45% management fee. KTCSX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. KTCSX, with annual returns of 10.43% over the last five years, is a well-diversified fund with a long track record of success.

MFS Mass Investors Growth Stock B (MIGBX Quick QuoteMIGBX - Free Report) is an attractive large-cap allocation. MIGBX 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. MIGBX has an expense ratio of 1.46%, management fee of 0.33%, and annual returns of 11.43% over the past five years.

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.