What Is an Index Fund? (Simple Beginner’s Guide)

Q: What's the difference between an index fund and an ETF?

An ETF is just a format -- like the difference between a paperback and a Kindle edition of the same book. An index fund can be either an ETF (like VOO, which trades on the stock exchange throughout the day) or a mutual fund (like VFIAX, which trades once per day at closing). Both track the same S&P 500 index and give you nearly identical returns. ETFs tend to have marginally lower fees and no minimum investment. For most people, it doesn't matter much which format you pick.

92% of professional money managers — people with finance degrees, Bloomberg terminals, and teams of analysts — failed to beat a simple S&P 500 index fund over the last 15 years. That’s not my opinion. That’s data from the SPIVA Scorecard, and it’s been consistent for decades. So when Warren Buffett tells everyone to just buy index funds, he’s not being humble. He’s being accurate. Here’s what index funds actually are, why they work so well, and how to buy your first one.

Index Funds in Plain English

An index fund is a basket of stocks that automatically mirrors a specific list of companies. The most famous list is the S&P 500 — the 500 biggest publicly traded companies in the US. Apple, Microsoft, Amazon, Google, Tesla, JPMorgan, Johnson & Johnson, the whole lineup.

When you buy an S&P 500 index fund, you’re buying tiny slivers of all 500 companies at once. Apple makes up about 7% of the index? Then 7% of your money goes into Apple. The overall index goes up 10%? Your investment goes up about 10%, minus a tiny fee that’s usually less than the spare change in your couch cushions.

Here’s how I think about it. Buying individual stocks is like going to 500 different stores trying to hand-pick the best products. Buying an index fund is like grabbing a pre-made variety pack that has a little of everything. Same exposure, about 1% of the effort.

Index funds come in two flavors. Index Mutual Funds trade once per day at the closing price and sometimes have minimum investments (though Fidelity’s ZERO funds have none). Index ETFs trade like stocks throughout the day — you can buy and sell anytime the market’s open, and fractional shares mean you can start with literally $1.

Curious what your index fund investments could grow to over 20-30 years? Plug some numbers into our Compound Interest Calculator and watch the curve.

Why Index Funds Crush Almost Everything Else

The evidence here isn’t subtle. It’s overwhelming.

They beat the professionals. That 92% figure from the SPIVA Scorecard? Let me make it even more concrete. If you’d handed $10,000 to a random actively managed fund 15 years ago, there was a 92% chance you’d have been better off just buying VOO and going to the beach. The pros don’t have a secret formula. After fees, most of them are just expensive ways to underperform.

They cost almost nothing. The Vanguard S&P 500 ETF (VOO) charges 0.03% per year. On $10,000, that’s $3. Three dollars. Fidelity’s FZROX charges 0.00% — literally free. Compare that to the average actively managed fund at 0.50%-1.50%, which would cost you $50-$150 per year on the same $10,000. Over 30 years on a growing portfolio, that fee difference can eat $30,000-$80,000 of your wealth. This blew my mind when I first ran the numbers.

Instant diversification. One purchase and you own 500 companies across tech, healthcare, finance, consumer goods, energy — everything. When Enron collapsed in 2001, S&P 500 index fund holders barely noticed because Enron was just one company out of 500. Try getting that kind of protection buying individual stocks.

The returns are legitimately great. The S&P 500 has averaged about 10.26% per year since 1957 (roughly 7% after inflation). In real dollars:

$10,000 invested in 1995 would be worth about $180,000 today. $10,000 invested in 2005: about $55,000. $10,000 invested in 2015: about $26,000. Even $10,000 invested right before the 2008 crash would have recovered and grown to over $45,000 by now.

Best Index Funds to Buy in 2025

Not all index funds are the same. Here are the ones actually worth your money.

S&P 500 Funds (US Large Companies)

Vanguard S&P 500 ETF (VOO): 0.03% expense ratio. Over $400 billion in assets. The gold standard. No minimum for the ETF.

Fidelity 500 Index Fund (FXAIX): 0.015% expense ratio — one of the cheapest S&P 500 funds anywhere. No minimum. Great if you’re already at Fidelity.

Schwab S&P 500 Index Fund (SWPPX): 0.02%, no minimum. Schwab’s version. Equally solid.

SPDR S&P 500 ETF Trust (SPY): 0.09%. The oldest and most heavily traded S&P 500 ETF. Slightly more expensive, but massive liquidity if that matters to you.

Total Stock Market Funds (Broader US Exposure)

Vanguard Total Stock Market ETF (VTI): 0.03%, tracks over 3,700 stocks including the small and mid-cap companies the S&P 500 misses. If you want the entire US stock market in one fund, this is it.

Fidelity ZERO Total Market Index Fund (FZROX): 0.00% expense ratio. Zero fees. No minimum. Honestly one of the best deals in all of investing.

International Funds

Vanguard Total International Stock ETF (VXUS): 0.08%, covers 7,800+ stocks outside the US. Adding 20-30% international to your portfolio is smart diversification.

For Canadian Investors

Vanguard S&P 500 Index ETF (VFV): 0.09%, CAD-denominated S&P 500 exposure.

iShares Core S&P/TSX Capped Composite (XIC): 0.06%, tracks the Canadian stock market.

Vanguard All-Equity ETF Portfolio (VEQT): 0.24%. This one’s a personal favorite — it’s a single fund holding stocks from 50+ countries including Canada, US, and international. One fund, global diversification, done.

For UK Investors

Vanguard FTSE Global All Cap Index Fund: 0.23%, tracks 7,000+ stocks globally. One-fund solution through Vanguard UK.

iShares Core MSCI World ETF (SWDA): 0.20%, developed market stocks worldwide.

Vanguard FTSE 100 Index Unit Trust: 0.06%, the 100 biggest UK companies. Good for home-country exposure if you want it.

Index Funds vs. Actively Managed Funds: The Honest Comparison

People still debate this, but the numbers really aren’t close.

Fees: Index funds cost 0.00%-0.20% per year. Actively managed funds cost 0.50%-2.00%. On $100,000 over 30 years at 10% returns, a 1% fee difference costs you approximately $300,000 in lost growth. That’s not a typo. Fees compound just like returns — except they compound against you.

Performance: Over 1 year, about 55% of active managers lose to the index. Over 5 years, roughly 75%. Over 15 years, 92%. Over 20+ years, around 95%. The longer you zoom out, the worse active management looks.

Taxes: Index funds trade rarely — maybe 3-5% annual turnover. Actively managed funds might turn over 50-100% of their holdings in a year, generating taxable events left and right. In a taxable account, this difference really adds up.

Simplicity: No worrying about a star manager leaving. No strategy changes. No research required. Buy, hold, rebalance once a year, done.

Even Buffett — the greatest active investor alive — told his estate to put 90% of his money into a low-cost S&P 500 index fund after he dies. He also won a famous million-dollar bet that an index fund would beat a basket of hedge funds over 10 years. The index fund returned 125.8%. The hedge funds averaged 36%. Wasn’t even competitive.

For a step-by-step walkthrough of putting your first dollars to work, read our guide on how to invest $1,000 as a beginner.

How to Buy Your First Index Fund (Takes About 15 Minutes)

This is genuinely not complicated.

In the US: Open a Roth IRA at Fidelity (my go-to recommendation for beginners — $0 minimums, zero-fee funds, great app). Transfer money from your bank. Search for VOO, VTI, or FZROX. Buy shares. Set up automatic monthly purchases. You’re done.

In Canada: Open a TFSA at Wealthsimple Trade (no commissions) or Questrade (free ETF purchases). Buy VFV, XIC, or VEQT. Set up auto-contributions.

In the UK: Open a Stocks and Shares ISA at Vanguard UK (lowest fees), AJ Bell, or Hargreaves Lansdown. Pick the FTSE Global All Cap fund or a LifeStrategy fund. Set up a monthly direct debit.

The whole thing — opening the account, transferring money, making your first purchase — takes 10-20 minutes. You can start with any amount. The important part is to start and then keep adding consistently. Use our Compound Interest Calculator to see what even modest monthly contributions turn into over a few decades.

Frequently Asked Questions

Can you lose money in an index fund?

Short term? Absolutely. The S&P 500 dropped 34% during COVID in 2020 and about 50% during the 2008 financial crisis. Those drops are real and they hurt. But here’s the thing — it’s recovered from every single one and gone on to new highs. Over any 20-year stretch in history, the S&P 500 has never delivered a negative return. So yes, you can lose money temporarily. If your timeline is 10+ years, history says you’ll be fine.

What’s the difference between an index fund and an ETF?

An ETF is just a format — like the difference between a paperback and a Kindle edition of the same book. An index fund can be either an ETF (like VOO, which trades on the stock exchange throughout the day) or a mutual fund (like VFIAX, which trades once per day at closing). Both track the same S&P 500 index and give you nearly identical returns. ETFs tend to have marginally lower fees and no minimum investment. For most people, it doesn’t matter much which format you pick.

How much money do I need to start?

Honestly? A dollar. Fidelity’s ZERO funds have no minimum. Fractional shares at most brokerages let you buy $5 of VOO if that’s what you’ve got. You don’t need $10,000 to get started. You don’t even need $100. Start with whatever you have and add to it over time. $50 or $100 a month in an index fund can turn into serious money given enough years.

Do I need more than one index fund?

For most beginners, one is honestly enough. A total stock market fund like VTI or a global fund like VEQT (Canada) or Vanguard FTSE Global All Cap (UK) already gives you massive diversification. As your portfolio grows past $10K-$20K, you might add an international fund or a small bond allocation. But don’t overcomplicate it early on. One solid index fund beats a confusing mix of five mediocre ones.

Are index funds good for retirement?

They’re arguably the best thing for retirement. Low fees mean more of your money actually compounds. Broad diversification means no single company can blow up your retirement. And the long-term returns speak for themselves. Most target-date retirement funds — the ones your 401(k) probably offers — are literally built out of index funds under the hood. If you’ve got 20-40 years, an index fund portfolio is really hard to beat.

The Boring Path to Wealth Actually Works

Index funds aren’t sexy. Nobody’s bragging about their Vanguard VTI position at a dinner party. There are no 10x overnight gains, no thrilling stock picks, no “I got in early on the next Tesla” stories. And that’s exactly the point.

$500 a month in an S&P 500 index fund at 10% average annual returns becomes roughly $1.1 million after 30 years. No stock picking. No market timing. No expensive advisor taking 1% off the top. Just consistency and compound interest doing what they’ve always done.

Open an account. Buy your first index fund. Set up automatic contributions. Check on it once or twice a year, mostly to rebalance. Use our Compound Interest Calculator to project where you’ll be in 10, 20, 30 years. The best time to start was a decade ago. The second best time is right now.