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.

Principal Mid Cap Value I R3 (PMPRX Quick QuotePMPRX - Free Report) : 1.19% expense ratio and 0.64% management fee. PMPRX is a Mid Cap Value fund, which usually invests in companies with a stock market valuation between $2 billion and $10 billion. With annual returns of 12.55% over the last five years, this fund is a winner.

Undiscovered Managers Behavioral Value L (UBVLX Quick QuoteUBVLX - Free Report) is a stand out amongst its peers. UBVLX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. With five-year annualized performance of 14.15%, expense ratio of 0.9% and management fee of 0.75%, this diversified fund is an attractive buy with a strong history of performance.

Vanguard Windsor Admiral (VWNEX Quick QuoteVWNEX - Free Report) . Expense ratio: 0.32%. Management fee: 0.28%. Five year annual return: 14.95%. VWNEX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value.

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.