What Are Index Funds and How Do They Work?

You've decided it's time to make your money work harder than a savings account can, but now you're wondering which company you should invest in. Apple? Nvidia? Tesla? While it may be tempting to simply pick the most popular option as a beginner, putting all your money into one company is like staking everything on one striker: if he has a bad game, so do you. Whether you earn a salary in naira, get paid in dollars by clients abroad or are setting aside your first few thousand naira, an index fund reduces risk. Instead of picking one company, you invest in hundreds at once, so your money moves with the whole market. In this guide, we'll explain what an index fund is, how it works, how it compares with ETFs and mutual funds, and how to start investing in one from Nigeria with as little as $2.

Key takeaways

• An index fund copies a list of companies, like the S&P 500 or the Nasdaq-100. When you invest in it, you own a small piece of every company on that list.
• One investment gets you hundreds of companies. Vanguard’s S&P 500 fund, VOO, holds 505, and its total market fund, VTI, holds 3,519.
• They’re hard to beat. Most professional fund managers who pick stocks earn less than the index, and in 2025, 79% of them did worse than the S&P 500.
• You can start in Nigeria with as little as $2. On Raenest, you can invest in a fraction of VOO, VTI or QQQM.
• They can still lose money. When the market falls, your fund falls too.

What is an index fund?

An index fund is an investment fund designed to track the performance of a market index. When you invest in one, you get exposure to the companies included in that index without having to buy their shares individually.

The US Securities and Exchange Commission (SEC) describes an index fund as a mutual fund or ETF that aims to replicate the returns of a particular market index.

To understand how this works, it helps to know what an index is. A market index is a group of selected stocks used to measure how a particular part of the stock market is performing.

For example, the S&P 500 tracks approximately 500 of the largest publicly traded US companies across sectors such as technology, healthcare, finance and consumer goods. The Nasdaq-100 tracks 100 of the largest non-financial companies listed on the Nasdaq exchange, with significant exposure to technology businesses such as Nvidia, Apple and Microsoft. If you're interested in the latter, our guide on how to invest in the Nasdaq-100 from Nigeria walks you through the process.

You can't invest directly in an index, just as you can't buy a chart or a list of companies. Instead, you buy a fund designed to follow it. For example, an S&P 500 index fund holds shares in the companies that make up the S&P 500. Rather than purchasing Apple, Microsoft, Nvidia, Amazon and hundreds of other stocks separately, you can get exposure to all of them through one investment.

However, your money isn't necessarily divided equally among these companies. Most major indexes use market capitalisation weighting, which means companies with larger market values account for a bigger portion of the fund. According to Vanguard's VOO fact sheet, as of 30 September 2026, Nvidia accounted for 8.4% of the fund, Apple 7.4% and Microsoft 5.8%. Together, the 10 largest holdings represented 40.6% of the portfolio.

This matters because owning an index fund doesn't mean every company has the same influence on your returns. The performance of larger holdings can have a greater effect on the fund's performance.

VOO is also an exchange-traded fund (ETF), meaning you can buy and sell it on a stock exchange, much like an individual stock. This brings us to an important distinction: index funds and ETFs aren't the same thing. An index fund describes an investment strategy, while an ETF describes how a fund is structured and traded. Some index funds are ETFs, while others are mutual funds.

If you're unfamiliar with ETFs, our guide to what an ETF is and how to start investing in one explains how they work. So how does a fund keep up with an index that keeps changing?

How do index funds work?

An index fund keeps up with its index by buying what the index holds, in the same proportions, and changing its holdings only when the index changes. It follows the same process every time:

1. The fund picks an index to follow. VOO follows the S&P 500, VTI follows the Morningstar US Total Market Index, which covers roughly every investable company in the US, and QQQ and QQQM follow the Nasdaq-100.
2. It buys the companies in that index. Some funds buy every company on the list, while others buy only a representative sample.
3. It matches each company's weight. If Nvidia is 8% of the index, it's roughly 8% of the fund.
4. It updates when the index updates. When a company joins or leaves the index, the fund buys or sells to match. Nobody is trying to guess the next winning stock, so trading stays low, and VOO replaced just 2.4% of its holdings in its most recent financial year.
5. Your return follows the index, minus fees. If the S&P 500 rises 10% in a year, an S&P 500 index fund should rise by about 10%, less its small annual fee. Over the 10 years to 30 September 2026, VOO returned 15.29% a year on average, compared with 15.33% for the S&P 500 itself. That tiny gap is a sign of a fund that tracks its index closely, so when you compare two funds that follow the same index, check how close each one stays to it over the long run.

Many index funds also pay dividends. When the companies in the fund share part of their profits, the fund passes that money on to you, usually every quarter. If you invest from Nigeria, the US withholds 30% of dividends paid to Nigerian investors, so you receive a little less than the headline yield.

Because the fund simply follows its index, the index you pick decides almost everything about your investment. That's where the different types of index funds come in.

Types of index funds and popular examples

Index funds come in as many flavours as there are indexes, and each type gives your money a different kind of exposure:

• Broad market funds cover almost the whole stock market of a country, including both large and small companies.
• Large-company funds follow only the biggest companies, like the S&P 500.
• Sector and theme funds follow one industry, such as technology or healthcare.
• International funds follow companies outside the US, in developed or emerging markets.
• Bond index funds follow a basket of government or company bonds instead of shares.

Before you pick one, look at what each fund tracks and who its biggest holdings are. VOO and QQQM both hold Nvidia, Apple and Microsoft, but an S&P 500 fund also spreads your money across banks, healthcare and energy, while a Nasdaq-100 fund leans much harder on tech. Once you know which one fits you, investing in it from Nigeria takes a few minutes.

How to invest in index funds from Nigeria

You can invest in US index funds from Nigeria through an app that gives you access to US-listed ETFs, and you don't need to live in the US or have a US bank account. Here's how to do it on Raenest, step by step.

1. Download the Raenest app and open an account. Get the app on the App Store or Google Play, create your account and complete identity verification.
2. Fund your Trading Wallet. Go to Stocks, tap Buy Stocks and move money in from your NGN, USD, GBP or EUR balance.
3. Search for the index fund. Type the ticker, such as VOO, VTI or QQQM, and open the fund page to check its fee and what it holds before you invest.
4. Enter your amount. You can start from $2, because Raenest supports fractional shares, so you don't need to buy a full share.
5. Place your order. The US market is open from 3:30 pm to 10 pm WAT between 1 November 2026 and 14 March 2027, and from 2:30 pm to 9 pm WAT while the US is on summer time. Orders you place outside these hours go through when the market opens.
6. Set up Auto-Invest. Choose a weekly or monthly schedule and an amount, and Raenest invests for you each time, so you keep investing consistently without having to remember.

Raenest gives you access to more than 4,000 US stocks and ETFs in the same app where you receive, send and manage your money. For an index fund investor, that means:

• A small starting amount. Start from $2 with fractional shares.
• Funding from your existing balance. Move money in from your NGN, USD, GBP or EUR balance.
• Auto-Invest on a weekly or monthly schedule.
• AI-powered summaries that help you follow what's moving in the market and in your portfolio.
• Regulated partners. Raenest's investment feature is offered with City Investment Capital Limited, a firm licensed by the SEC Nigeria, and your US investments are held with Alpaca Securities LLC, a member of FINRA and SIPC.

🔗 For a full walkthrough, read How to Buy U.S. Stocks and ETFs from Nigeria: A Complete Guide (2026).

Ready to own a piece of hundreds of companies at once? Start investing in index funds on Raenest today, from $2.

Index funds vs ETFs vs mutual funds vs individual stocks

If you've been reading about ETFs and mutual funds alongside index funds, you've probably noticed the terms overlap. That's because "index fund" describes a strategy (copy an index), while "ETF" and "mutual fund" describe how a fund is packaged and traded. VOO, for example, is both an index fund and an ETF.

Not every ETF is an index fund, though. Some ETFs are actively managed, with a team choosing what to buy. And not every index fund is an ETF, because some are mutual funds, which you can only buy or sell at one price at the end of each trading day. Here's how they compare side by side:

If you're investing from Nigeria, the simplest way to own a US index fund is through an index ETF, because you can invest in it the same way you'd invest in a single share, even in fractions. Here's more on how fractional shares work. With the differences clear, here's why so many investors choose index funds in the first place.

Why do people invest in index funds?

People choose index funds because they're cheap, spread out and hard to beat over time. Here's what that means for your money.

1. You don't put all your eggs in one basket. If one company in the S&P 500 has a terrible year, it's one of about 500, so your money isn't riding on a single CEO's decisions.
2. The fees are small, and small fees add up. Vanguard's fact sheet shows VOO charging 0.03% a year, while the average S&P 500 index fund charges 0.41%. On $1,000, that's $0.30 against $4.10 every year, and the gap grows as your money grows. As the SEC points out, when two funds perform the same, the cheaper one generally leaves you with higher returns. So when two funds follow the same index, like QQQM at 0.15% and QQQ at 0.18%, the lower fee usually wins for long-term investors.
3. Most professionals struggle to beat the index. S&P Dow Jones Indices tracks this every six months, and its latest SPIVA scorecard found that 79% of active large-cap US funds underperformed the S&P 500 in 2025, and 67% did in the first half of 2026. Investing in the index gets you the market's return without having to find the rare manager who beats it.
4. You don't need to study stocks every day. The index decides what's in the fund. You decide how much to invest and how often.
5. It suits small, regular amounts. With fractional shares, you can invest a few dollars and keep adding every week or month. Investing a fixed amount on a schedule means you invest on good and bad market days instead of trying to time the perfect moment, which is one of the long-term investment habits every Nigerian should start today.
6. It gives naira earners exposure to US dollar assets. US index ETFs are priced in dollars, so your investment's value is measured in dollars.

Start investing in index funds on Raenest today

If you're new to investing, an index fund is one of the simplest, lowest-cost ways to start. Instead of betting everything on one company, you spread your money across hundreds of them, so one bad stock can't wipe out your savings. You don't need to know which company will win next, and you don't need a lot of money to begin. On Raenest, you can invest in VOO, VTI, QQQM and QQQ from just $2, fund your investment straight from your NGN, USD, GBP or EUR balance, and set up Auto-Invest so your money keeps working every week or month. Every month you wait is another month your money isn't growing.

Start investing in VOO, VTI, QQQM and QQQ on Raenest today.

Frequently asked questions

1. Are index funds good for beginners?

Yes. Index funds are one of the most common starting points for new investors because one purchase gives you hundreds of companies, the fees are low, and you don't need to pick individual stocks. You still need to accept that the value will go up and down.

2. Is an index fund the same as an ETF?

Not always. An index fund copies a market index, while an ETF is any fund that trades on a stock exchange. Many index funds are ETFs, like VOO and VTI, but some index funds are mutual funds, and some ETFs are actively managed.

3. How much do I need to invest in index funds from Nigeria?

You can start from $2 on Raenest, because you can buy a fraction of an ETF share instead of a whole one. You can fund your Trading Wallet from your NGN, USD, GBP or EUR balance.

4. Can I lose money in an index fund?

Yes. An index fund rises and falls with the market it tracks, and there's no guaranteed return. Investing for five years or more, adding money regularly and only using money you won't need soon can help you ride out the bad years.

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Disclaimer: Raenest is not a broker-dealer, investment adviser or member of FINRA. Securities offered by Alpaca Securities LLC ("Alpaca Securities"). Alpaca Securities is a member of FINRA and the Securities Investor Protection Corporation. Raenest does not recommend any specific securities or investment strategies. Investing involves risk & investments may lose value, including the loss of principal. Past performance does not guarantee future results. Investors should consider their investment objectives and risks carefully before investing. U.S. stock investments are held with Alpaca Securities LLC, a U.S.-licensed broker-dealer regulated by the SEC and FINRA. Your assets are custodied under strict regulatory and security standards, and you retain full visibility into your holdings and performance at all times. The investment feature is offered in partnership with City Investment Capital Limited, a firm licensed by the Securities and Exchange Commission of Nigeria.

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