It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

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

Nationwide Bailard Cognitive Value M (NWHFX Quick QuoteNWHFX - Free Report) : 0.94% expense ratio and 0.75% management fee. NWHFX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. With annual returns of 10.72% over the last five years, this fund is a winner.

AQR Global Equity Fund R6 (AQGRX Quick QuoteAQGRX - Free Report) . Expense ratio: 0.7%. Management fee: 0.6%. AQGRX is a Global - Equity mutual fund, which invests their assets in large markets, leveraging the global economy. This fund has managed to produce a robust 10.89% over the last five years.

Hartford Dividend & Growth HLS IA (HIADX Quick QuoteHIADX - Free Report) : 0.66% expense ratio and 0.63% management fee. HIADX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. With a five-year annual return of 12.85%, 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.