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 break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Thrivent Large Cap Value Fund A (AAUTX Quick QuoteAAUTX - Free Report) : 0.85% expense ratio and 0.45% management fee. AAUTX is a Large Cap Value fund. These funds invest in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. AAUTX has achieved five-year annual returns of an astounding 12.4%.

RBB Free Market US Equity (FMUEX Quick QuoteFMUEX - Free Report) : 0.55% expense ratio and 0.49% management fee. FMUEX is an All Cap Growth mutual fund. In order to increase diversification, these funds have holdings across small, medium, and large-cap levels. FMUEX, with annual returns of 11.41% over the last five years, is a well-diversified fund with a long track record of success.

TIAA-CREF Small Cap Equity Premier (TSRPX Quick QuoteTSRPX - Free Report) : 0.57% expense ratio and 0.4% management fee. TSRPX is a Small Cap Blend mutual fund, and usually targets stocks with market caps of less than $2 billion, letting investors diversify their funds among other kinds of small-cap equities. With a five-year annual return of 10.21%, this fund is a well-diversified fund with a long track record of success.

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.