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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

JPMorgan US Equity Fund R5 (JUSRX): 0.54% expense ratio and 0.4% management fee. JUSRX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset. With annual returns of 17.1% over the last five years, this fund is a winner.

GMO US Small Cap Value VI (GCAVX Quick QuoteGCAVX - Free Report) . Expense ratio: 0.47%. Management fee: 0.37%. GCAVX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. This fund has managed to produce a robust 16.96% over the last five years.

Loomis Sayles Global Growth N (LSNGX): 0.9% expense ratio and 0.75% management fee. LSNGX is a Global - Equity mutual fund, which invests their assets in large markets, leveraging the global economy. With a five-year annual return of 12.71%, this fund is a well-diversified fund with a long track record of success.

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.