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 easiest, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. The Zacks Mutual Fund Rank, which covers over 19,000 mutual funds, has helped us identify three outstanding options that are perfect for any long-term investors' portfolios that is retirement-focused.

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 Black Oak Emerging Technology Fund (BOGSX Quick QuoteBOGSX - Free Report) . With a much more diversified approach, BOGSX--part of the Sector - Tech mutual fund category--gives investors a way to own a stake in the notoriously risky tech sector. This fund is a winner, boasting an expense ratio of 1%, management fee of 0.74%, and a five-year annualized return track record of 12.71%.

Fidelity Growth Discovery K (FGDKX Quick QuoteFGDKX - Free Report) . Expense ratio: 0.68%. Management fee: 0.6%. FGDKX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. This fund has managed to produce a robust 12.84% over the last five years.

Neuberger Berman Small Cap Growth Trust (NBMOX Quick QuoteNBMOX - Free Report) : 1.25% expense ratio and 1.23% management fee. NBMOX is one of many Small Cap Growth mutual funds; these funds tend to create their portfolios around stocks with market capitalization of less than $2 billion. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.76% over the last five years.

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.