Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

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

Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

Fidelity Select Health Care Services (FSHCX Quick QuoteFSHCX - Free Report) : 0.73% expense ratio and 0.53% management fee. FSHCX is part of the Sector - Health category, offering investors a focus on the healthcare industry, one of the largest sectors in the American economy. With annual returns of 11.81% over the last five years, this fund is a winner.

TIAA-CREF Small Cap Equity Premier (TSRPX Quick QuoteTSRPX - Free Report) . Expense ratio: 0.57%. Management fee: 0.4%. TSRPX is a Small Cap Blend mutual fund, and usually targets stocks with market caps of less than $2 billion, letting investors diversify their funds among other kinds of small-cap equities. This fund has managed to produce a robust 11.73% over the last five years.

T. Rowe Price US Large-Cap Core Adviser (PAULX Quick QuotePAULX - Free Report) is an attractive large-cap allocation. PAULX 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. PAULX has an expense ratio of 0.93%, management fee of 0.54%, and annual returns of 14.02% over the past five years.

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.