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 way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund Rank of over 19,000 mutual funds, we've identified three outstanding mutual funds that are ideally suited to help long-term investors pursue and achieve their retirement investing goals.

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

Fidelity Series Opportunistic Insights (FVWSX Quick QuoteFVWSX - Free Report) : 0.27% expense ratio and 0% management fee. FVWSX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. FVWSX has achieved five-year annual returns of an astounding 11.56%.

JPMorgan Mid Cap Growth Fund R2 (JMGZX Quick QuoteJMGZX - Free Report) : 1.45% expense ratio and 0.65% management fee. JMGZX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion. With yearly returns of 11.05% over the last five years, JMGZX is an effectively diversified fund with a long reputation of solidly positive performance.

Elfun Trusts (ELFNX Quick QuoteELFNX - Free Report) . Expense ratio: 0.18%. Management fee: 0.14%. Five year annual return: 13.49%. ELFNX 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.

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.