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.

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

Pioneer International Value A (PIIFX): 1.13% expense ratio and 0.65% management fee. PIIFX 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. PIIFX has achieved five-year annual returns of an astounding 12.13%.

Goldman Sachs Large Cap Value Insights IR (GCVTX Quick QuoteGCVTX - Free Report) : 0.67% expense ratio and 0.52% management fee. GCVTX 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. With yearly returns of 11.79% over the last five years, GCVTX is an effectively diversified fund with a long reputation of solidly positive performance.

DWS Equity Sector Strategy C (SUPCX). Expense ratio: 1.48%. Management fee: 0.28%. Five year annual return: 11.15%. SUPCX is classified as an Allocation Balanced fund, which seeks to invest in a balance of asset types, like stocks, bonds, and cash, and including precious metals or commodities is not unusual.

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.