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 take a look at some of our top-ranked mutual funds with the lowest fees.

AQR Global Equity Fund I

(AQGIX Quick QuoteAQGIX - Free Report) : 0.8% expense ratio and 0.6% management fee. AQGIX is a Global - Equity mutual fund investing in bigger markets like the U.S., Europe, and Japan; these kinds of funds aren't limited by geography. With annual returns of 12.71% over the last five years, this fund is a winner.

DFA US Small Cap Value I

(DFSVX Quick QuoteDFSVX - Free Report) : 0.31% expense ratio and 0.28% management fee. DFSVX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. DFSVX, with annual returns of 15.73% over the last five years, is a well-diversified fund with a long track record of success.

Invesco Comstock R6

(ICSFX Quick QuoteICSFX - Free Report) : 0.45% expense ratio and 0.38% management fee. ICSFX 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. With a five-year annual return of 14.62%, 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.