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.

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

Hood River Small Cap Growth Institutional (HRSMX Quick QuoteHRSMX - Free Report) : 1.05% expense ratio and 0.9% management fee. HRSMX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. HRSMX has achieved five-year annual returns of an astounding 14.3%.

ProFunds UltraBull Fund Investor (ULPIX Quick QuoteULPIX - Free Report) is a stand out amongst its peers. ULPIX 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. With five-year annualized performance of 15.13%, expense ratio of 1.41% and management fee of 0.75%, this diversified fund is an attractive buy with a strong history of performance.

Fidelity Convertible Securities (FCVSX Quick QuoteFCVSX - Free Report) . Expense ratio: 0.73%. Management fee: 0.51%. Five year annual return: 12.28%. FCVSX is categorized as a Convertible Bonds fund, and in the fixed income world, these funds are quite unique. These types of securities are a hybrid, meaning they have components of both fixed income and equity.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.