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 take a look at some of our top-ranked mutual funds with the lowest fees.

JPMorgan Developed Intl Value I (JIESX) has a 0.74% expense ratio and 0.55% management fee. JIESX is a part of the Non US - Equity fund category, many of which will focus across all cap levels, and will typically allocate their investments between emerging and developed markets. With yearly returns of 15.12% over the last five years, this fund clearly wins.

Boston Partners Global Equity Institutional (BPGIX Quick QuoteBPGIX - Free Report) : 0.95% expense ratio and 0.9% management fee. BPGIX is a Global - Equity mutual fund investing in bigger markets like the U.S., Europe, and Japan; these kinds of funds aren't limited by geography. With yearly returns of 11.42% over the last five years, BPGIX is an effectively diversified fund with a long reputation of solidly positive performance.

O'Shaughnessey MarketLeadersValue I (OFVIX): 0.55% expense ratio and 0.41% management fee. OFVIX 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. With a five-year annual return of 13%, 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.