Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

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 break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Franklin Small Cap Growth R6 (FSMLX Quick QuoteFSMLX - Free Report) : 0.67% expense ratio and 0.62% management fee. FSMLX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. FSMLX has achieved five-year annual returns of an astounding 8.57%.

RBC SMID Cap Growth A (TMCAX Quick QuoteTMCAX - Free Report) is a stand out amongst its peers. TMCAX 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 five-year annualized performance of 10.78%, expense ratio of 1.07% and management fee of 0.7%, this diversified fund is an attractive buy with a strong history of performance.

T. Rowe Price Growth Stock Fund (PRGFX Quick QuotePRGFX - Free Report) . Expense ratio: 0.65%. Management fee: 0.51%. Five year annual return: 12.63%. PRGFX 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.

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.