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.

Pioneer Fundamental Growth A (PIGFX Quick QuotePIGFX - Free Report) : 0.98% expense ratio and 0.61% management fee. PIGFX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. PIGFX has achieved five-year annual returns of an astounding 12.22%.

Putnam Equity Income R5 (PEQLX Quick QuotePEQLX - Free Report) . Expense ratio: 0.65%. Management fee: 0.47%. PEQLX 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. This fund has managed to produce a robust 10.27% over the last five years.

Principal Capital Appreciation I (PWCIX Quick QuotePWCIX - Free Report) : 0.46% expense ratio and 0.44% management fee. PWCIX 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. With a five-year annual return of 11.79%, this fund is a well-diversified fund with a long track record of success.

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.