What is Mutual Fund? (Plain English Definition)
A mutual fund is an investment vehicle that pools money from many investors to buy a diversified portfolio of securities, priced once daily after market close.
Last updated: April 2026
Definition: A mutual fund is an investment vehicle that pools money from many investors to buy a diversified portfolio of securities, priced once daily after market close.
Mutual Fund Explained Simply
A mutual fund collects money from many investors and uses it to buy a diversified portfolio of stocks, bonds, or other securities. Unlike ETFs, mutual fund shares are not traded on an exchange. Instead, you buy and sell shares directly from the fund company at the net asset value (NAV) calculated once per day after the market closes.
Mutual funds have been around much longer than ETFs and still hold more total assets. They come in both actively managed versions (where a manager picks investments) and index versions (which track a benchmark). Historically, mutual funds have been the dominant retirement account investment, partly because many employer 401(k) plans offer mutual funds but not ETFs.
The main differences between mutual funds and ETFs include: ETFs trade throughout the day while mutual funds trade once daily; ETFs generally have lower expense ratios; ETFs are more tax-efficient due to their creation/redemption mechanism; and ETFs have no minimum investment beyond the price of one share. However, mutual funds have some advantages -- they allow automatic investing of exact dollar amounts, and they never have bid-ask spreads.
Mutual Fund Example
You invest $3,000 in the Vanguard 500 Index Fund (VFIAX), a mutual fund that tracks the S&P 500 with a 0.04% expense ratio. You place the order at 2 PM, but it executes at the NAV calculated after market close at 4 PM. The comparable Vanguard S&P 500 ETF (VOO) has a 0.03% expense ratio and can be bought at any time during market hours. Both track the same index, but the ETF is slightly cheaper and more flexible.
Why Mutual Fund Matters for ETF Investors
Understanding mutual funds helps ETF investors appreciate the advantages ETFs offer and make informed choices between the two. For taxable accounts, ETFs are almost always the better choice due to lower costs and superior tax efficiency. For retirement accounts like 401(k)s where ETFs may not be available, low-cost index mutual funds are excellent alternatives. For ETF investors, knowing about mutual funds is practical because many people have both. You might use ETFs in your brokerage account while owning mutual funds in your employer's retirement plan. Understanding both vehicles helps you coordinate your overall investment strategy and avoid unnecessary duplication or gaps in your portfolio.
Mutual Fund vs Exchange-Traded Fund
| Mutual Fund | Exchange-Traded Fund |
|---|---|
| A mutual fund is an investment vehicle that pools money from many investors to buy a diversified portfolio of securities, priced once daily after market close. | See full definition of Exchange-Traded Fund |
While mutual fund and exchange-traded fund are related concepts, they serve different purposes when picking and evaluating ETFs. Understanding both terms helps you make more informed decisions about which funds to include in your portfolio and how to evaluate their performance.
Related Terms
Deepen your understanding of ETF investing by exploring these related concepts:
Exchange-Traded Fund
An exchange-traded fund (ETF) is a basket of securities that trades on a stock exchange just like an individual stock.
Index Fund
An index fund is a type of investment fund designed to match the performance of a specific market index, such as the S&P 500.
Net Asset Value (NAV)
Net asset value (NAV) is the per-share value of a fund calculated by dividing the total value of all its holdings minus liabilities by the number of outstanding shares.
Expense Ratio
The expense ratio is the annual fee an ETF charges its shareholders, expressed as a percentage of your investment.
Open-End Fund
An open-end fund continuously issues and redeems shares at NAV based on investor demand, unlike closed-end funds which have a fixed number of shares.
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