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.

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 retirement investors' portfolios.

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

AB Growth & Income Adviser

(CBBYX Quick QuoteCBBYX - Free Report) : 0.64% expense ratio and 0.55% management fee. CBBYX 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. With annual returns of 11.34% over the last five years, this fund is a winner.

Fidelity Fund K

(FFDKX Quick QuoteFFDKX - Free Report) : 0.37% expense ratio and 0.32% management fee. FFDKX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset. FFDKX, with annual returns of 16.78% over the last five years, is a well-diversified fund with a long track record of success.

JPMorgan Large Cap Growth R2

(JLGZX Quick QuoteJLGZX - Free Report) : 1.19% expense ratio and 0.45% management fee. JLGZX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 18.41% 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.