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.

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

MFS Mass Investors Growth Stock R6 (MIGNX Quick QuoteMIGNX - Free Report) : 0.37% expense ratio and 0.33% management fee. MIGNX 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. MIGNX has achieved five-year annual returns of an astounding 13.44%.

Vanguard Windsor-II Admiral (VWNAX Quick QuoteVWNAX - Free Report) : 0.26% expense ratio and 0.25% management fee. VWNAX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. With yearly returns of 9.98% over the last five years, VWNAX is an effectively diversified fund with a long reputation of solidly positive performance.

Invesco Small Cap Value Y (VSMIX Quick QuoteVSMIX - Free Report) . Expense ratio: 0.83%. Management fee: 0.64%. Five year annual return: 8.66%. VSMIX is a Small Cap Value mutual fund, investing in small companies with stock market valuation less than $2 billion.

There you have it. If your financial advisor had you put your money into any of our top-ranked funds, then they've got you covered. If not, you may need to talk.