What Is a Mutual Fund? A Plain-English Guide

What exactly is a mutual fund?#

The SEC's Investor.gov site describes a mutual fund as an SEC-registered open-end investment company that pools money from many investors^[1]. The fund uses that pool to buy stocks, bonds, short-term money-market instruments or a mix of these^[2]. Each share you own represents part ownership of the fund's whole portfolio^[1].

Open-end means the fund keeps issuing and buying back shares. FINRA explains that the fund creates new shares to meet demand and buys back shares from investors who want to sell^[3]. This is different from a closed-end fund, which raises money once and then trades on an exchange like a stock^[3].

In the U.S., mutual funds are regulated under the Investment Company Act of 1940. That law focuses on disclosure: telling investors about the fund and its objectives. It does not let the SEC judge whether a fund's investments are good ones^[4]. Rules differ by country, so if you invest outside the U.S., check your local regulator.

How a mutual fund works

Money flows in from many investors, a registered adviser invests it, and each share tracks the value of the whole pool.

How is a mutual fund's price set?#

A mutual fund does not have a price that moves all day like a stock. Instead it calculates its net asset value (NAV): total assets minus total liabilities, divided by the number of shares outstanding^[5]. U.S. mutual funds generally must calculate NAV at least once every business day, typically after the major U.S. exchanges close^[5].

When you place an order, you get the next NAV calculated after the order, plus any purchase fees^[1]. That means you do not know the exact price when you click buy. The SEC's guide lists this as a drawback: the fund might not calculate NAV until many hours after you place the order^[2]. For a full definition see net asset value.

Worked example

Worked example: from portfolio value to your shares

An illustrative fund holds $102.5 million of assets and owes $2.5 million in liabilities, with 8 million shares outstanding. Its NAV is $12.50 per share. A $5,000 order with no sales charge buys 400 shares. With a 5% front-end load, a $10,000 check pays a $500 charge, the same size as the SEC's own example^[6], so only $9,500 is invested.

Step	Amount
Net assets ($102.5M − $2.5M)	$100,000,000
NAV per share (÷ 8,000,000 shares)	$12.50
$5,000, no load: shares bought	400.000
$10,000 with 5% front-end load: charge	$500.00
$10,000 with 5% load: amount invested	$9,500.00
$10,000 with 5% load: shares bought	760.000
If assets rise 1% the next day: new NAV	$12.63

Figures computed in code from the stated inputs; rounded to the nearest cent or tenth.

How do mutual fund investors make or lose money?#

Investor.gov lists three ways a fund can pay off. The fund may earn income such as dividends on stocks or interest on bonds. It may sell a security that rose in price, which is a capital gain. And if the market value of the portfolio rises after expenses and liabilities, the NAV rises^[1].

The same mechanics work in reverse. If the holdings fall, NAV falls. Mutual funds are not guaranteed or insured by the FDIC or any other government agency, and you may lose some or all of the money you invest^[1]. That is true even if you buy through a bank and the fund carries the bank's name^[2].

What kinds of mutual funds are there?#

Most funds fall into a few broad families. The SEC's Investor.gov groups them like this^[1]:

Common types of mutual funds and what they mainly hold
Fund type	What it mainly holds	Read more
Stock (equity) fund	Stocks	What is a stock?
Bond (income) fund	Bonds and other debt securities	Bond funds vs individual bonds
Money market fund	Liquid, short-term debt, cash and cash equivalents	What is a bond?
Target date fund	A mix of stock funds, bond funds and other funds	Asset allocation basics
Index fund	Securities in a chosen market index	Index funds explained

Fund types from Investor.gov^[1]; index funds from the SEC's index fund bulletin^[8].

An index fund can be a mutual fund or an exchange-traded fund; it simply aims to track a market index^[8]. A fund's name is only a hint. The SEC warns that you should not rely on a fund's name without examining the prospectus^[9].

What does a mutual fund cost?#

There are two layers. Shareholder fees are charged directly to you, for example a front-end load when you buy or a back-end load when you sell. Annual fund operating expenses are regular, fund-wide costs^[6]. Added together and shown as a percentage of average net assets, the operating expenses are the expense ratio^[6].

Many funds sell several share classes of the same portfolio with different fee setups. FINRA describes Class A shares as charging a front-end sales charge, Class B shares as usually charging a deferred charge if you sell within a certain period, and Class C shares as often charging about 1% if you sell within a short time^[3]. Larger purchases can qualify for lower front-end loads at levels called breakpoints^[3]. So-called 12b-1 fees, paid from fund assets for marketing and selling, are capped at 1% of your assets in the fund^[3].

Mutual fund fee facts from U.S. regulators

SEC example: 5% front-end load on $10,000: $500^[6]
12b-1 fee cap (FINRA): 1% of your assets in the fund^[3]
Typical Class C sell charge (FINRA): Often 1% if sold within a short time^[3]
Where fees are listed: The prospectus fee table^[6]

Investor.gov puts it plainly: even small differences in fees can mean large differences in returns over time^[1]. FINRA's online Fund Analyzer lets you compare expenses across funds and share classes^[3]. Our fee drag calculator shows the effect of a yearly cost on any balance.

Why do people use mutual funds, and what are the trade-offs?#

The SEC's guide to funds lists the main reasons. Most funds are run by investment advisers registered with the SEC. Spreading money across many companies or sectors can help lower risk if one company or sector fails; see diversification. Some funds accept small starting amounts, and you can redeem shares on any business day at the next NAV^[2].

The same guide lists the trade-offs: you pay fees and expenses regardless of how the fund performs, you cannot choose which securities the fund holds, and you do not know your exact trade price in advance^[2]. If you want intraday trading, compare with exchange-traded funds or read ETF vs mutual fund.

What mistakes do beginners make?#

Judging a fund by its name
A name like "Growth" or "Income" is not a full description. Read the objective, strategies and principal risks in the prospectus before buying; our prospectus guide shows where to look.
Thinking a bank-sold fund is insured
A mutual fund bought at a bank is still an investment, not a deposit. It is not FDIC-insured and can lose value.
Ignoring the share class
The same portfolio can cost very different amounts in Class A, B or C shares. Check loads, 12b-1 fees and the expense ratio for the exact class you are offered.
Expecting the price you see at order time
A mutual fund order fills at the next NAV, usually set after the market closes, not at yesterday's NAV shown on screen.

What else do beginners ask?#

Can I lose money in a mutual fund?

Yes. Mutual funds are not guaranteed or insured by the FDIC or any other government agency, and you may lose some or all of what you invest^[1].

When does my mutual fund order get its price?

At the next net asset value calculated after the fund receives your order. In the U.S. that is generally once each business day, typically after the major exchanges close^[5].

Is a mutual fund the same as an index fund?

Not always. An index fund is one style of fund that tries to track a market index, and it can be a mutual fund or an ETF^[8]. Many mutual funds are actively managed instead.

Where do I find a fund's fees?

In the fee table near the front of the prospectus, which lists shareholder fees and annual operating expenses^[6].

What is the bottom line?#

A mutual fund is a shared portfolio: many investors put money in, a registered adviser invests it, and each share rises or falls with the whole pool. The price is set once a day at NAV, costs come from loads and yearly expenses, and nothing about the structure protects you from market losses. Read the prospectus, check the fee table for the share class you are offered, and compare before you buy.

What is a mutual fund, and how does buying one actually work?