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.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

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

MFS Mass Investors Growth Stock A (MIGFX Quick QuoteMIGFX - Free Report) has a 0.71% expense ratio and 0.33% management fee. MIGFX 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 11.73% over the last five years, this fund clearly wins.

T. Rowe Price Health Sciences I (THISX Quick QuoteTHISX - Free Report) : 0.67% expense ratio and 0.63% management fee. THISX is a Sector - Health mutual fund, which give investors an opportunity to focus on healthcare, one of the largest sectors of the American economy. With yearly returns of 9.57% over the last five years, THISX is an effectively diversified fund with a long reputation of solidly positive performance.

Victory Sycamore Established Value I (VEVIX Quick QuoteVEVIX - Free Report) : 0.58% expense ratio and 0.45% management fee. VEVIX is a Mid Cap Value mutual funds that aims to target medium-sized companies that possess strong value and income opportunities for investors. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.09% over the last 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.