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.

Oppenheimer Discovery Y (ODIYX Quick QuoteODIYX - Free Report) has a 0.82% expense ratio and 0.6% management fee. ODIYX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With yearly returns of 10.74% over the last five years, this fund clearly wins.

Principal Large Cap Growth I R1 : 1.47% expense ratio and 0.6% management fee. PCRSX 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. PCRSX, with annual returns of 13.59% over the last five years, is a well-diversified fund with a long track record of success.

T. Rowe Price US Equity Research (PRCOX Quick QuotePRCOX - Free Report) . Expense ratio: 0.44%. Management fee: 0.33%. Five year annual return: 15.97%. PRCOX is classified as a Large Cap Blend fund. More often than not, Large Cap Blend mutual funds invest in companies with a market cap of over $10 billion. Buying stakes in bigger companies offer these funds more stability, and are well-suited for investors with a "buy and hold" mindset.

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.