Our "Magnificent Retirement Mutual Funds" list includes some of the best managed and best performing funds around. If you're already invested in these, congratulations! But if you're just now discovering them, don't worry. When it comes to your retirement, it's never too late to start investing in the best.

The easiest, most reliable way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Our Zacks Rank 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.

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

Principal Large Cap Growth I R3 (PPUMX Quick QuotePPUMX - Free Report) : 1.16% expense ratio and 0.6% management fee. PPUMX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. With annual returns of 12.95% over the last five years, this fund is a winner.

T. Rowe Price Mid-Cap Growth Adviser (PAMCX Quick QuotePAMCX - Free Report) : 1.03% expense ratio and 0.61% management fee. PAMCX is a Mid Cap Growth mutual fund. Mid Cap Growth funds pick stocks--usually companies with a market cap between $2 billion and $10 billion--that demonstrate extensive growth opportunities for investors compared to their peers. PAMCX, with annual returns of 10.34% over the last five years, is a well-diversified fund with a long track record of success.

AB Small Cap Growth I (QUAIX Quick QuoteQUAIX - Free Report) : 0.9% expense ratio and 0.75% management fee. QUAIX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With a five-year annual return of 14.11%, this fund is a well-diversified fund with a long track record of success.

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.

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.