If you're invested in any of the funds in our "Magnificent Retirement Mutual Funds" list, congratulations on owning some of the best managed and top-performing mutual funds. If you are lucky enough to discover our list of Top-Ranked Funds for the first time, it's never too late to start investing with the best, especially when it comes to your retirement.

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.

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

MFS Growth R6 (MFEKX Quick QuoteMFEKX - Free Report) has a 0.56% expense ratio and 0.54% 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 11.75% over the last five years, this fund clearly wins.

Fidelity Select Medical Equipment & Systems (FSMEX Quick QuoteFSMEX - Free Report) . Expense ratio: 0.71%. Management fee: 0.54%. FSMEX is a Sector - Health mutual fund, which give investors an opportunity to focus on healthcare, one of the largest sectors of the American economy. This fund has managed to produce a robust 11.47% over the last five years.

MSIF Global Opportunity Portfolio A (MGGPX Quick QuoteMGGPX - Free Report) . Expense ratio: 1.22%. Management fee: 0.74%. Five year annual return: 11.84%. MGGPX is a Global - Equity mutual fund. These funds invest in large markets like the U.S., Europe, and Japan, and operate with very few geographical limitations.

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.

Do You Know the Top 9 Retirement Investing Mistakes?

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.