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.

Pioneer Fundamental Growth R (PFGRX Quick QuotePFGRX - Free Report) has a 1.4% expense ratio and 0.61% management fee. PFGRX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. With yearly returns of 11.83% over the last five years, this fund clearly wins.

RBC SMID Cap Growth I (TMCIX Quick QuoteTMCIX - Free Report) : 0.82% expense ratio and 0.7% management fee. TMCIX is a Mid Cap Growth mutual fund. These funds aim to target companies with a market capitalization between $2 billion and $10 billion that are also expected to exhibit more extensive growth opportunities for investors than their peers. With yearly returns of 10.49% over the last five years, TMCIX is an effectively diversified fund with a long reputation of solidly positive performance.

Vanguard Diversified Equity Investor (VDEQX Quick QuoteVDEQX - Free Report) is an attractive large-cap allocation. VDEQX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. VDEQX has an expense ratio of 0.35%, management fee of 0%, and annual returns of 10.2% over the past five years.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.