It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

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 investors' portfolios.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

If you are looking to diversify your portfolio, consider Pioneer International Value Y (INVYX). INVYX is a Non US - Equity fund. Many of these funds like to allocate across emerging and developed markets, and will often focus on all cap levels. This fund is a winner, boasting an expense ratio of 0.74%, management fee of 0.65%, and a five-year annualized return track record of 10.53%.

Fidelity Blue Chip Growth Fund (FBGRX Quick QuoteFBGRX - Free Report) . Expense ratio: 0.61%. Management fee: 0.6%. FBGRX 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 12.14% over the last five years.

American Funds Washington Mutual Investors R5 (RWMFX). Expense ratio: 0.31%. Management fee: 0.22%. Five year annual return: 11.58%. RWMFX 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.