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 investors' portfolios.

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

Transamerica Large Core R4 (TLAFX): 0.8% expense ratio and 0.45% management fee. TLAFX 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 11.6% over the last five years, this fund is a winner.

Pioneer International Value Y (INVYX). Expense ratio: 0.74%. Management fee: 0.65%. INVYX is a Non US - Equity fund. Many of these funds like to allocate across emerging and developed markets, and will often focus on all cap levels. This fund has managed to produce a robust 10.53% over the last five years.

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, which invests their assets in large markets, leveraging the global economy. With a five-year annual return of 11.42%, 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.