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 investors' portfolios.

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

If you are looking to diversify your portfolio, consider Goldman Sachs Capital Growth Service Class (GSPSX). GSPSX 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 is a winner, boasting an expense ratio of 1.2%, management fee of 0.69%, and a five-year annualized return track record of 10.58%.

Vanguard Energy Investor (VGENX). Expense ratio: 0.45%. Management fee: 0.43%. VGENX is a Sector - Energy mutual fund, which encompasses a wide range of vastly changing and vitally important industries throughout this massive global sector. This fund has managed to produce a robust 19.75% over the last five years.

Invesco Technology R6 (FTPSX Quick QuoteFTPSX - Free Report) : 0.65% expense ratio and 0.58% management fee. FTPSX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 12.28% over the last five years.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.