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.

If you are looking to diversify your portfolio, consider Brown Advisory Sustainable Growth Investor (BIAWX Quick QuoteBIAWX - Free Report) . BIAWX 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. This fund is a winner, boasting an expense ratio of 0.78%, management fee of 0.53%, and a five-year annualized return track record of 12.45%.

Fidelity Advisor Technology M (FATEX Quick QuoteFATEX - Free Report) : 1.21% expense ratio and 0.52% management fee. FATEX is part of the Sector - Tech mutual fund category that invests in technology and lets investors own a stake in a notoriously volatile sector, but with a much more diversified approach. FATEX, with annual returns of 13.46% over the last five years, is a well-diversified fund with a long track record of success.

Oberweis Small-Cap Opportunities (OBSOX Quick QuoteOBSOX - Free Report) . Expense ratio: 1.25%. Management fee: 0.8%. Five year annual return: 15.48%. OBSOX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets.

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.