There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

BNY Mellon Natural Resources A (DNLAX Quick QuoteDNLAX - Free Report) : 1.14% expense ratio and 0.75% management fee. DNLAX is classified as a Sector - Energy mutual fund. Throughout the massive global energy sector, these funds hold a wide range of quickly changing and vitally important industries. With annual returns of 14.25% over the last five years, this fund is a winner.

Neuberger Berman Guardian Institutional (NGDLX Quick QuoteNGDLX - Free Report) is a stand out amongst its peers. NGDLX 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. With five-year annualized performance of 11.47%, expense ratio of 0.68% and management fee of 0.63%, this diversified fund is an attractive buy with a strong history of performance.

Pioneer Fundamental Growth R (PFGRX Quick QuotePFGRX - Free Report) . Expense ratio: 1.4%. Management fee: 0.61%. Five year annual return: 10.33%. PFGRX 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.

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.