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.

Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

If you are looking to diversify your portfolio, consider Sterling Capital Equity Income I (BEGIX Quick QuoteBEGIX - Free Report) . BEGIX 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. This fund is a winner, boasting an expense ratio of 0.79%, management fee of 0.55%, and a five-year annualized return track record of 10.8%.

Calvert Equity Portfolio A (CSIEX Quick QuoteCSIEX - Free Report) . Expense ratio: 0.91%. Management fee: 0.55%. CSIEX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. This fund has managed to produce a robust 12.84% over the last five years.

Fidelity Select Health Care Services (FSHCX Quick QuoteFSHCX - Free Report) . Expense ratio: 0.71%. Management fee: 0.52%. Five year annual return: 11.87%. FSHCX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.