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

MFS Mass Investors Growth Stock C (MIGDX Quick QuoteMIGDX - Free Report) : 1.46% expense ratio and 0.33% management fee. MIGDX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. With annual returns of 10.73% over the last five years, this fund is a winner.

T. Rowe Price New Horizons I (PRJIX Quick QuotePRJIX - Free Report) . Expense ratio: 0.65%. Management fee: 0.63%. PRJIX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. This fund has managed to produce a robust 10.34% over the last five years.

Virtus KAR Small-Cap Core I (PKSFX Quick QuotePKSFX - Free Report) is an attractive large-cap allocation. PKSFX is a Small Cap Blend mutual fund that usually targets companies with a market capitalization of less than $2 billion. PKSFX has an expense ratio of 0.99%, management fee of 0.75%, and annual returns of 12.44% 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.