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.

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.

AMG Frontier Small Cap Growth N (MSSVX Quick QuoteMSSVX - Free Report) has a 1.3% expense ratio and 0.7% management fee. MSSVX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With yearly returns of 9.44% over the last five years, this fund clearly wins.

American Funds Investor Company of America R6 (RICGX Quick QuoteRICGX - Free Report) : 0.27% expense ratio and 0.23% management fee. RICGX 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. RICGX, with annual returns of 9.8% over the last five years, is a well-diversified fund with a long track record of success.

ClearBridge Large Cap Growth I (SBLYX Quick QuoteSBLYX - Free Report) is an attractive large-cap allocation. SBLYX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. SBLYX has an expense ratio of 0.78%, management fee of 0.61%, and annual returns of 10.41% over the past five years.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.