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, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

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

If you are looking to diversify your portfolio, consider Neuberger Berman Guardian R3 (NGDRX Quick QuoteNGDRX - Free Report) . NGDRX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. This fund is a winner, boasting an expense ratio of 1.36%, management fee of 0.74%, and a five-year annualized return track record of 14.53%.

Alger Capital Appreciation Focus Z (ALZFX Quick QuoteALZFX - Free Report) : 0.61% expense ratio and 0.52% management fee. ALZFX 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. ALZFX, with annual returns of 14.63% over the last five years, is a well-diversified fund with a long track record of success.

Ivy Mid Cap Growth N (IGRFX Quick QuoteIGRFX - Free Report) : 0.79% expense ratio and 0.77% management fee. IGRFX 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 a five-year annual return of 15.37%, this fund is a well-diversified fund with a long track record of success.

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.