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.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term investors' portfolios.

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

American Funds Washington Mutual Investors R1 (RWMAX Quick QuoteRWMAX - Free Report) : 1.35% expense ratio and 0.22% management fee. RWMAX 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. RWMAX has achieved five-year annual returns of an astounding 11.13%.

Thornburg Global Opportunities R6 (THOGX): 0.85% expense ratio and 0.83% management fee. THOGX 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. THOGX, with annual returns of 13.43% over the last five years, is a well-diversified fund with a long track record of success.

Selected American Shares D (SLADX) is an attractive large-cap allocation. SLADX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. SLADX has an expense ratio of 0.65%, management fee of 0.55%, and annual returns of 10.97% over the past five years.

There you have it. If your financial advisor had you put your money into any of our top-ranked funds, then they've got you covered. If not, you may need to talk.