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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

Janus Henderson Global Life Science D (JNGLX Quick QuoteJNGLX - Free Report) : 0.8% expense ratio and 0.64% management fee. JNGLX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy. With annual returns of 11.96% over the last five years, this fund is a winner.

MFS Mass Investors Growth Stock R4 (MIGKX Quick QuoteMIGKX - Free Report) : 0.46% expense ratio and 0.33% management fee. MIGKX 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. With yearly returns of 12.23% over the last five years, MIGKX is an effectively diversified fund with a long reputation of solidly positive performance.

Oberweis Small-Cap Opportunities (OBSOX Quick QuoteOBSOX - Free Report) : 1.25% expense ratio and 0.8% management fee. OBSOX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With a five-year annual return of 14.41%, this fund is a well-diversified fund with a long track record of success.

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.