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.

T. Rowe Price Mid-Cap Value (TRMCX Quick QuoteTRMCX - Free Report) has a 0.8% expense ratio and 0.64% management fee. TRMCX is a Mid Cap Value mutual fund, which targets medium-sized companies with a market cap between $2 billion and $10 billion. With yearly returns of 11.61% over the last five years, this fund clearly wins.

Fidelity Advisor Stock Select Allocation Cap M (FSJHX Quick QuoteFSJHX - Free Report) : 1.13% expense ratio and 0.46% management fee. FSJHX 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. With yearly returns of 13.24% over the last five years, FSJHX is an effectively diversified fund with a long reputation of solidly positive performance.

Janus Henderson Contrarian R (JCNRX Quick QuoteJCNRX - Free Report) : 1.46% expense ratio and 0.6% management fee. JCNRX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 12.67% over the last five years.

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.