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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

AMG River Road Focused Absol Val I (AFAVX Quick QuoteAFAVX - Free Report) : 0.82% expense ratio and 0.6% management fee. AFAVX is a Mid Cap Value fund, which usually invests in companies with a stock market valuation between $2 billion and $10 billion AFAVX has achieved five-year annual returns of an astounding 11.34%.

Carillon Clarivest Intl Stock I (EISIX): 0.95% expense ratio and 0.7% management fee. EISIX is a Non US - Equity fund. Many of these funds like to allocate across emerging and developed markets, and will often focus on all cap levels. EISIX, with annual returns of 14.83% over the last five years, is a well-diversified fund with a long track record of success.

American Funds Income Fund of America R5 (RIDFX) is an attractive large-cap allocation. RIDFX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. RIDFX has an expense ratio of 0.29%, management fee of 0.23%, and annual returns of 10.71% 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.