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.

RBB Free Market US Equity (FMUEX Quick QuoteFMUEX - Free Report) has a 0.55% expense ratio and 0.49% management fee. FMUEX is an All Cap Growth mutual fund with holdings across small, medium, and large-cap levels in order to increase diversification. With yearly returns of 9.93% over the last five years, this fund clearly wins.

American Century Growth A (TCRAX Quick QuoteTCRAX - Free Report) : 1.18% expense ratio and 0.97% management fee. TCRAX 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. TCRAX, with annual returns of 16.17% over the last five years, is a well-diversified fund with a long track record of success.

Westwood Large Cap Value Fund I (WHGLX Quick QuoteWHGLX - Free Report) : 0.64% expense ratio and 0.5% management fee. WHGLX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 9.25% over the last 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.