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 1.01% 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 11.12% over the last five years, this fund clearly wins.

Fidelity Advisor Technology I (FATIX Quick QuoteFATIX - Free Report) : 0.71% expense ratio and 0.52% management fee. FATIX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. FATIX, with annual returns of 14.18% over the last five years, is a well-diversified fund with a long track record of success.

Principal Blue Chip Fund I (PBCKX Quick QuotePBCKX - Free Report) . Expense ratio: 0.65%. Management fee: 0.59%. Five year annual return: 11.02%. PBCKX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers.

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.