It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

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.

Buffalo Small Cap Fund (BUFSX Quick QuoteBUFSX - Free Report) has a 1% expense ratio and 0.85% management fee. BUFSX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With yearly returns of 11.72% over the last five years, this fund clearly wins.

Janus Henderson Global Life Science T (JAGLX Quick QuoteJAGLX - Free Report) . Expense ratio: 0.91%. Management fee: 0.64%. JAGLX is classified as a Sector - Health fund. Healthcare is one of the biggest sectors of the American economy, and these kinds of mutual funds provide a great opportunity to invest in this industry. This fund has managed to produce a robust 10.19% over the last five years.

T. Rowe Price New America Growth Adviser (PAWAX Quick QuotePAWAX - Free Report) is an attractive large-cap allocation. PAWAX 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. PAWAX has an expense ratio of 1.06%, management fee of 0.63%, and annual returns of 12.48% 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.