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.

The easiest, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

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

If you are looking to diversify your portfolio, consider American Funds Fundamental Investors R3 (RFNCX). RFNCX 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. This fund is a winner, boasting an expense ratio of 0.92%, management fee of 0.24%, and a five-year annualized return track record of 13.46%.

T. Rowe Price Emerging Mkts Val Stk (PRIJX). Expense ratio: 1.13%. Management fee: 0.93%. PRIJX is a Non US - Equity option, focusing their investments acoss emerging and developed markets, and can often extend across cap levels too. This fund has managed to produce a robust 10.31% over the last five years.

GMO-Usonian Japan Value Creation VI (GMAHX Quick QuoteGMAHX - Free Report) . Expense ratio: 0.6%. Management fee: 0.56%. Five year annual return: 12.9%. GMAHX is part of the Japan - Equity category, which mostly invest in Japan-based companies; Japan is one of the world's richest and most diversified economies.

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.