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.

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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

Neuberger Berman Small Cap Growth Trust (NBMOX Quick QuoteNBMOX - Free Report) : 1.25% expense ratio and 1.23% management fee. NBMOX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With annual returns of 12.78% over the last five years, this fund is a winner.

Vanguard PRIMECAP Fund Investor (VPMCX Quick QuoteVPMCX - Free Report) . Expense ratio: 0.38%. Management fee: 0.37%. VPMCX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. This fund has managed to produce a robust 10.79% over the last five years.

Hartford Dividend & Growth R6 (HDGVX Quick QuoteHDGVX - Free Report) : 0.63% expense ratio and 0.6% management fee. HDGVX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.11% 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.