There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

The best way to shortlist great mutual funds is to ensure solid performance, diversification, and low fees. Some are better than others, but utilizing the Zacks Mutual Fund Rank, we have identified three mutual funds that could be solid additions to one's retirement portfolio.

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 Ivy Large Cap Growth Y (WLGYX Quick QuoteWLGYX - Free Report) . WLGYX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. This fund is a winner, boasting an expense ratio of 1%, management fee of 0.6%, and a five-year annualized return track record of 11.07%.

Janus Henderson Global Life Science T (JAGLX Quick QuoteJAGLX - Free Report) . Expense ratio: 0.91%. Management fee: 0.64%. JAGLX is a Sector - Health mutual fund, which give investors an opportunity to focus on healthcare, one of the largest sectors of the American economy. This fund has managed to produce a robust 10.19% over the last five years.

Oberweis Small-Cap Opportunities (OBSOX Quick QuoteOBSOX - Free Report) . Expense ratio: 1.25%. Management fee: 0.8%. Five year annual return: 17.2%. OBSOX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets.

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.