The funds in our "Magnificent Retirement Mutual Funds" list are among the best managed and best performing mutual funds available. If you are just finding out about our Top-Ranked Funds list, we welcome you!

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 our Zacks Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

MFS Growth R6 (MFEKX Quick QuoteMFEKX - Free Report) has a 0.57% expense ratio and 0.55% management fee. MFEKX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. With yearly returns of 14.61% over the last five years, this fund clearly wins.

T. Rowe Price Media & Telecomm (PRMTX Quick QuotePRMTX - Free Report) : 0.76% expense ratio and 0.64% management fee. PRMTX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. With yearly returns of 14.25% over the last five years, PRMTX is an effectively diversified fund with a long reputation of solidly positive performance.

Fidelity Advisor Small Cap Growth A (FCAGX Quick QuoteFCAGX - Free Report) : 1.32% expense ratio and 0.84% management fee. FCAGX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 12.69% over the last five years.

There you have it. If your financial advisor had you put your money into any of our "Magnificent Retirement Mutual Funds," then they've got you covered. If not, you may need to talk.

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Investing in underperforming mutual funds is just one of the key errors that can derail your retirement plans.

To learn more, read our just-released report: 9 Retirement Mistakes You Need to Avoid.