Every payday, I do the same small thing. I open my brokerage app, and with a single tap, I buy a tiny piece of 500 of the biggest companies in America — Apple, Microsoft, Coca-Cola, Amazon, and hundreds more. It takes about ten seconds.
For a long time, I did this without really understanding what I was buying. I just knew smart people kept saying “buy the S&P 500,” so I did. Then one day a coworker asked me, “So what actually is the S&P 500?” — and I realized I couldn’t explain it clearly. If I couldn’t, I figured a lot of other people couldn’t either.
So let me explain it the way I wish someone had explained it to me: simply, honestly, and without the jargon.
The S&P 500 Is a List, Not a Thing You Buy
Here’s the first thing that confused me, so let’s clear it up right away.
The S&P 500 is not a company. It’s not a product. You can’t actually buy “the S&P 500” directly. It’s a list — specifically, a list of about 500 of the largest publicly traded companies in the United States.
Think of it like a sports league’s ranking of the top 500 teams. The ranking itself isn’t a team you can join; it’s a measuring stick that tells you how those top teams are doing as a group. The S&P 500 does the same thing for big American companies. When you hear on the news that “the S&P 500 was up today,” it means those 500 companies, taken together, were worth a little more than yesterday.
The name makes sense once you know it: “S&P” comes from Standard & Poor’s, the company that created the index, and “500” is roughly how many companies are on the list.
How a Company Actually Gets on the List
“The 500 biggest American companies” is the shorthand, and it’s close enough for most conversations. But it isn’t quite right, and the real answer is more interesting.
There is no automatic ranking. A committee at S&P Dow Jones Indices decides who goes in and who comes out, and candidates have to clear a set of published hurdles first. As of 2026, the main ones are:
- Size. A market capitalization of at least about $22.7 billion. That bar is reviewed every quarter and has climbed steadily over the years.
- Actual profits. The company must have positive earnings over its most recent four quarters combined, and in the most recent quarter on its own. This is the screen that keeps enormous but loss-making companies out.
- Enough shares in public hands. At least 10% of shares must be freely tradable, and the publicly available portion has to be worth roughly half the size threshold on its own.
- Liquidity. A minimum of 250,000 shares traded in each of the six months before review.
- A US listing. Primary listing on the NYSE, Nasdaq, or Cboe.
The full rulebook is public — you can read the S&P U.S. Indices methodology document yourself.
Two things follow from this that I think are worth sitting with.
First, the profitability screen means the index is not simply “the biggest companies.” It’s closer to “the biggest companies that have demonstrated they can make money.” That’s a quiet quality filter running in the background of my monthly purchase, and I didn’t know it existed for the first several years I was buying.
Second, because a committee decides, the list is a judgment call, not a law of nature. Companies get added after they’ve already grown enormous, which means the index often buys them at high prices rather than on the way up. That’s a genuine criticism of index investing, and I’d rather you hear it from me than discover it later and wonder what else I left out.
Why 500 Companies Matter So Much
You might wonder: why do people care so much about this one particular list?
Because those 500 companies are giants. Together, they make up roughly 80% of the total value of the entire U.S. stock market. So even though there are thousands of public companies in America, this single list of 500 captures the vast majority of the action.
That’s why the S&P 500 is often treated as a stand-in for “the U.S. economy” or “the market” as a whole. When people ask “how did the market do today?”, they’re usually looking at the S&P 500.
One important detail: not every company on the list counts equally. The index is what’s called “market-cap weighted,” which is a fancy way of saying bigger companies get a bigger say. A massive company like Apple moves the index far more than the 400th-largest company on the list. So when a few tech giants have a great day, the whole index tends to rise with them.
Not All 500 Count Equally
This is the single most important thing I misunderstood for years, so I want to be blunt about it.
The S&P 500 is weighted by size. It is not 500 companies at 0.2% each. The bigger the company, the more of the index it represents — so when you buy an S&P 500 fund, your money is very far from evenly spread.
How far? By 2026 the ten largest companies account for somewhere in the region of 37% to 40% of the entire index, depending on the day you measure. Between 1990 and 2015 that figure sat comfortably between about 18% and 23%. It has roughly doubled in a decade, driven by a handful of megacap technology and AI-linked companies.
Put plainly: buying “500 companies” currently means putting something like four dollars in every ten into ten companies, most of them in the same industry, and the remaining six dollars across the other 490.
I still buy it. But I want to be honest that “diversified” is doing a lot of work in that sentence, and it is doing less work than it did when I started. If technology has a bad decade, the index will have a bad decade, and no amount of describing it as “the whole market” will change that.
This is also why I hold a few things alongside it rather than putting every dollar in one index — not because I think I can outsmart anyone, but because I’d rather not have one story decide my entire outcome.
How Do You Actually Invest in It, Then?
If you can’t buy the list itself, how do millions of people “invest in the S&P 500”?
The answer is index funds and ETFs. These are simple investment products designed to copy the list. When you put money into an S&P 500 index fund, that fund quietly goes out and buys small slices of all 500 companies for you, in the right proportions. You get the whole basket in one purchase.
This is exactly what I do. I don’t hand-pick stocks. Every month, I put a fixed amount into a fund that tracks the S&P 500, and in one tap I own a sliver of all 500 companies. If Apple soars, I benefit a little. If one company stumbles, the other 499 cushion the blow. That built-in spreading-out is called diversification, and for a busy person like me, it’s the whole appeal.
Which Fund, and What It Actually Costs
Since you can’t buy the list itself, the practical question is which fund you use to copy it. In the US, three dominate, and the difference between them is smaller than the internet suggests.
Those links go to each provider’s own product page. I don’t use affiliate or referral links anywhere on this site, so there’s nothing in it for me whichever one you look at.
What does the cost difference actually mean? On $10,000 invested, 0.03% is about $3 a year and 0.0945% is about $9.45 a year. Six dollars. It is real, it compounds over decades, and it is also nowhere near the most important decision you will make. Consistency matters more than six dollars.
One note for readers outside the US, because I’m one of them: I don’t actually buy VOO. Inside a Korean retirement account, I buy a locally listed fund that tracks the same index, because that’s what the tax-advantaged wrapper allows. The index is the same. The container is different. If you’re investing from outside the US, check what your own retirement accounts permit before assuming you need the American ticker.
S&P 500 vs. Nasdaq 100 vs. the Dow
These three get mentioned in the same breath on the news, which makes them sound interchangeable. They aren’t.
| Holdings | Weighted by | |
|---|---|---|
| S&P 500 | About 500 US large caps | Company size |
| Nasdaq 100 | 100 Nasdaq non-financials | Company size, capped |
| Dow Jones | 30, picked by committee | Share price |
The Dow is the one people quote and the one that tells you least — 30 companies weighted by share price is a method nobody would design today; it survives because it’s old and famous. The Nasdaq 100 is a bet on a narrower slice of the economy, which is thrilling in some decades and painful in others.
The S&P 500 sits between them, and that unremarkable middle position is exactly why it’s the one I build around.
The Track Record (and an Honest Warning)
Now for the part everyone wants to know: does it actually make money?
Historically, yes — over the long run. Since the modern S&P 500 was introduced in 1957, it has returned roughly 10% per year on average. That average is the reason the index has such a loyal following.
But — and this is a big but — that 10% is a long-term average, not a promise, and definitely not what happens every year. Some years the S&P 500 soars 25%. Other years it falls 20%, 30%, or more. It has lived through brutal crashes: the dot-com bust, the 2008 financial crisis, the 2020 pandemic drop. Anyone who tells you the stock market only goes up is not being honest with you.
The reason long-term investors stay calm through the scary years is that, historically, the index has always eventually recovered and gone on to new highs. “Historically” is doing a lot of work in that sentence, though — the past can’t guarantee the future. That’s the honest truth, and I’d rather tell you the honest truth than a comforting story.
Questions I Get Asked
Is it 500 companies, or 503?
Both, sort of. The index targets 500 companies, but a few of them have more than one class of shares listed, so the number of actual holdings usually runs slightly above 500. It changes. Nothing about your investment depends on it.
Can I buy the S&P 500 from outside the United States?
Almost certainly yes. Most countries have locally listed funds tracking the same index, and many can be held inside domestic tax-advantaged accounts. That’s how I do it from Korea. Check what your own retirement accounts allow first — the tax treatment usually matters more than the ticker.
Does the S&P 500 include dividends?
The headline number you see on the news is the price index, which excludes dividends. The total return version — what you actually earn if you reinvest — is meaningfully higher over long periods. When people quote long-run returns of around 10% a year, they are usually quoting total return.
Isn’t it risky to put everything in one country?
It’s a fair objection, and I don’t have a knockdown answer. The counter-argument is that these companies earn a large share of their revenue outside the US, so you get more international exposure than the label implies. The honest version is that I’ve accepted a concentration in one country’s largest firms, and I know it.
What’s the difference between an index fund and an ETF?
Mostly how you buy it. An ETF trades on an exchange like a share, throughout the day. A traditional index fund is priced once daily. Both can track the same index at nearly the same cost. Don’t let this distinction hold you up.
Why This Boring List Is the Backbone of My Plan
I’m a 40-something engineer, not a Wall Street trader. I don’t have time to analyze companies, and I’ve made peace with the fact that I’m probably not going to out-smart the market.
So I’ve built my plan around this boring, beautiful list instead. Every month, a fixed amount goes in. I own a piece of 500 of America’s biggest companies. I don’t panic when it drops, and I don’t celebrate when it jumps. I just keep buying, month after month, and let time do the heavy lifting.
It’s not exciting. But after years of chasing “exciting,” I’ve come to believe that boring and consistent is exactly what builds a six-figure dream.
In my next post, I’ll explain the simple strategy I use to buy it — investing the same amount every single month, no matter what the market is doing. It’s called dollar-cost averaging, and it’s the reason I sleep well at night.
A quick, honest note: I’m not a financial advisor, and nothing here is personalized investment advice. I’m just an ordinary person sharing what I’m learning and doing. Please do your own research, and consider speaking with a qualified professional before making any investment decisions.
— Steve