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.

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

MFS Blended Research Value Equit R6

(BRUNX Quick QuoteBRUNX - Free Report) : 0.42% expense ratio and 0.4% management fee. BRUNX 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 annual returns of 11.52% over the last five years, this fund is a winner.

Janus Henderson Global Technology and Innovation T

(JAGTX Quick QuoteJAGTX - Free Report) . Expense ratio: 0.89%. Management fee: 0.64%. JAGTX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. This fund has managed to produce a robust 18.66% over the last five years.

Principal Mid Cap J

(PMBJX Quick QuotePMBJX - Free Report) is an attractive large-cap allocation. PMBJX is a Mid Cap Growth mutual fund. These funds aim to target companies with a market capitalization between $2 billion and $10 billion that are also expected to exhibit more extensive growth opportunities for investors than their peers. PMBJX has an expense ratio of 0.78%, management fee of 0.58%, and annual returns of 11.99% 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.