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.

Fidelity Advisor Value Strategies M (FASPX Quick QuoteFASPX - Free Report) has a 1.39% expense ratio and 0.68% management fee. FASPX is a Global - Equity mutual fund, which invests their assets in large markets, leveraging the global economy. With yearly returns of 11.93% over the last five years, this fund clearly wins.

John Hancock Disciplined Value R6 (JDVWX Quick QuoteJDVWX - Free Report) is a stand out amongst its peers. JDVWX 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. With five-year annualized performance of 10.88%, expense ratio of 0.65% and management fee of 0.61%, this diversified fund is an attractive buy with a strong history of performance.

Principal Mid Cap R3 (PMBMX Quick QuotePMBMX - Free Report) . Expense ratio: 1.15%. Management fee: 0.58%. Five year annual return: 10.5%. PMBMX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion.

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.