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.

DFA US Large Cap Equity Institutional (DUSQX Quick QuoteDUSQX - Free Report) : 0.13% expense ratio and 0.1% management fee. DUSQX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. DUSQX has achieved five-year annual returns of an astounding 10.52%.

Pioneer Fundamental Growth Y (FUNYX Quick QuoteFUNYX - Free Report) . Expense ratio: 0.75%. Management fee: 0.61%. FUNYX 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. This fund has managed to produce a robust 12.55% over the last five years.

Invesco Small Cap Value Y (VSMIX Quick QuoteVSMIX - Free Report) : 0.83% expense ratio and 0.64% management fee. VSMIX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. With a five-year annual return of 10.07%, 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.