Buying many companies at once is the easy part. The difference between two funds that look identical can stay with you for thirty years.
Published on August 26, 2026 · by Alex · Guide · Getting started · ETF
An ETF is a fund that pools stocks, bonds or other assets and trades on an exchange like a share. To choose one, define the exposure you need first; then compare its index, concentration, annual cost, tracking difference, liquidity, domicile and whether it accumulates or distributes income. The best ETF is the one that performs that job with costs and risks you understand.
Two ETFs can carry “S&P 500” in their names, show almost the same return and charge a difference that looks microscopic. The problem is that the difference is deducted every year, including from money that would itself have earned a return. Over thirty years it stops being microscopic. But before costs can be compared, a more important question has to be answered: what are you actually buying?
ETF means exchange-traded fund. It pools money from many investors, uses it to hold a portfolio of shares, bonds or other assets, and divides that portfolio into units traded throughout the day like a share. Each unit represents proportional ownership of the portfolio and the income it generates, according to the SEC's 2023 investor guide.
Not every ETF does the same job. Some track an index; others are actively managed. Some physically own the underlying securities; others obtain part of their exposure through derivatives. And an ETF is not the same as every product traded on an exchange: an ETN, for example, is debt issued by a financial institution and adds the issuer's credit risk. The legal structure in the prospectus matters before the ticker does.
| Vehicle | What you buy | How it trades |
|---|---|---|
| Share | Part of one company | Throughout the day on an exchange |
| ETF | Part of a pooled portfolio | Throughout the day on an exchange |
| Mutual fund | Part of a pooled portfolio | Usually at net asset value calculated at the close |
| ETN | A payment promise from an issuer | Throughout the day on an exchange |
The wrapper explains how you buy. What determines how your money behaves is what sits inside, and that starts with the index.
An index is a set of rules for building a list and assigning weights. It is not a neutral portfolio. The S&P 500 contains 500 leading large US companies and covers about 80% of the market capitalisation available in that market, according to S&P Dow Jones Indices. That makes it broad within large US companies, not within the whole world.
The Nasdaq-100 measures one hundred of the largest non-financial companies with a primary Nasdaq listing. The methodology effective from May 2026 excludes the financial industry. By design, therefore, it is neither “the US economy” nor “the whole technology sector”: it is a selection determined by exchange, size and eligibility rules.
A global large- and mid-cap equity index adds developed and emerging markets. That brings in thousands of companies and several regions, but “global” does not mean equally divided. In the Vanguard FTSE All-World UCITS ETF, for example, the United States represented 61.62% and the fund held 3,782 stocks on July 31, 2026. Those figures move with the market and should be checked in the current factsheet.
| Index type | Main exposure | What it leaves out or reduces |
|---|---|---|
| S&P 500 | Large US companies | Smaller companies and most other countries |
| Nasdaq-100 | Large non-financial Nasdaq-listed companies | Financials and companies listed on other exchanges |
| Broad global | Developed and emerging markets | May omit small companies and still carries a large US weight |
The useful question is not which one won over the last five years. It is which exposure you want to hold for the next ten and how much of it you already own. Counting companies alone cannot answer that.
Not necessarily. Diversification depends on the weight of every position, sector, country and source of risk, not only on the number of names. A market-cap-weighted index gives more room to the companies with the greatest stock-market value. If those companies rise faster than the rest, the index becomes more concentrated automatically.
The top ten holdings make this visible. They represented 37.6% of the S&P 500 on August 21, 2026, according to S&P Dow Jones Indices. In the global Vanguard fund cited above, the ten largest positions added up to about 23.5% on July 31, 2026, calculated from Vanguard's holdings. Both figures will change: the point is to inspect the block before buying, not to memorise it.
Overlap matters too. Buying one S&P 500 ETF and one Nasdaq-100 ETF does not necessarily split a portfolio into two different halves: many of their largest companies appear in both. The second fund can increase precisely the exposure it appeared to diversify.
Quick test: open the fund factsheet, add the ten largest holdings and check the largest country and sector. If you would not accept that distribution written out as a portfolio, the number of companies does not repair it.
Once what the fund owns is settled, the cost of holding it becomes meaningful. That is where the small difference from the opening returns.
The expense ratio, TER or OCF is the annual percentage deducted from assets to run the fund. It does not arrive as an invoice: it slowly reduces the investment's value. The SEC notes that a higher-cost fund must perform better than a lower-cost fund to leave the investor with the same net return.
A mathematical example, not a forecast: if $10,000 grew at 7% gross a year for thirty years, it would end at roughly $75,485 with a 0.03% cost, $71,968 with a 0.20% cost and $57,435 with a 1% cost. The gap between 0.03% and 1% exceeds $18,000 even when the underlying asset is identical. The calculation uses annual compounding with no contributions, taxes, spreads or inflation.
That does not make the cheapest fund an automatic winner. Compare funds seeking the same exposure and inspect their tracking difference: the gap between the fund's actual return and its index after costs, internal withholding, sampling and transactions. The accumulating Vanguard FTSE All-World UCITS ETF reported annualised tracking error of 0.07% over one and three years as of July 31, 2026. That is historical evidence, not a guarantee.
And the published annual charge is not the whole cost. The missing part appears when units are bought and sold.
The SEC's July 2025 fund-cost guide separates fund expenses from transaction costs that do not appear in the prospectus fee table. A comparison needs the full set:
The spread may be close to zero in a heavily traded ETF and much wider in a thinly traded product. The SEC gives a deliberately clear example: buying 200 units at $60 and immediately selling at $59.50 produces a $100 loss from the spread alone. A limit order lets the investor set a maximum buying price or a minimum selling price, although execution is not guaranteed.
Liquidity is not fully captured by the volume on screen either. Both the market for ETF units and the liquidity of the underlying assets matter. For a long-term holder, TER and tracking repeat every year; for someone who trades often, spreads, commissions and conversion can dominate. One final choice determines what happens to the income.
An accumulating class retains and reinvests net dividends or interest inside the fund. A distributing class pays them to the investor at the stated frequency. The 2026 iShares II prospectus says that distributing classes may pay net income, while accumulating classes make no distribution and reinvest income and other profits.
| Class | What happens to income | When it may fit |
|---|---|---|
| Accumulating | Reinvested inside the fund | When the aim is continued accumulation without manual reinvestment |
| Distributing | Paid periodically | When cash flow is wanted or the investor wants to choose its destination |
Distribution does not create extra return: when cash leaves the fund, its value adjusts for the payment. Accumulation does not universally avoid tax. Some countries tax income even when reinvested; others distinguish between classes, fund domiciles or account types. Withholding may also occur within the chain before income reaches the fund.
The correct tax question therefore contains three facts: your tax residence, the ETF's legal domicile and its distribution policy. The currency shown beside the ticker answers none of them.
Not by itself. The same fund can trade in dollars, euros, pounds or pesos while holding exactly the same portfolio. Trading currency is the unit used to buy on that exchange; economic currency exposure comes from the currencies in which the underlying assets create value and from whether the share class is currency hedged.
The distributing Vanguard FTSE All-World factsheet, for example, showed USD, GBP, CHF, EUR and MXN listings in August 2026 carrying the same Irish ISIN. Buying the euro line does not turn the fund's US and Japanese companies into European assets.
To identify the investment, record at least the full name, ISIN, share class, domicile, index, exchange and trading currency. A ticker can change between exchanges; the ISIN identifies the same class. With those facts collected, a comparison no longer depends on marketing.
This checklist closes the hidden cost opened in the first paragraph. It was not only the printed percentage: it was a charge compounding for decades, plus index slippage and the cost of entering and leaving. The right ETF is not the one with the lowest isolated number, but the one that delivers the chosen exposure through a structure and total cost you can explain.
Nothing in this guide is financial, legal or tax advice. It is a method for reading documents and comparing equivalent vehicles. Fees, portfolios and rules carry dates because they change: check the current prospectus, factsheet and local rules before making a decision.
Main sources consulted: SEC ETF guide (Feb. 23, 2023); SEC fund and ETF costs (July 23, 2025); FINRA, exchange-traded products; S&P 500; Nasdaq-100 methodology effective May 1, 2026; Vanguard FTSE All-World UCITS ETF, data at July 31, 2026; iShares II plc, 2026 prospectus.
An ETF is a pooled portfolio that can hold shares, bonds or other assets and whose units trade on an exchange throughout the day. Buying a unit does not make you the direct owner of every underlying security: it gives you proportional ownership of the fund and of the income generated by its portfolio.
None is best for everyone. The S&P 500 concentrates on large US companies; the Nasdaq-100 holds large non-financial companies listed on Nasdaq and has a stronger sector tilt; a global index adds developed and emerging markets, although the United States can still represent more than half. The right choice depends on the exposure missing from your portfolio.
Start with the annual expense ratio, TER or OCF, but do not stop there. Also check tracking difference against the index, the bid-ask spread, brokerage charges, currency conversion and custody costs. Two funds with the same published fee can leave investors with different results.
An accumulating share class reinvests income inside the fund; a distributing class pays it to investors periodically. Accumulation simplifies reinvestment, while distribution provides cash flow. Neither is universally more tax-efficient: treatment depends on your tax residence, the fund domicile and the rules currently in force.
Yes. A diversified ETF reduces dependence on a single company, but it does not remove market risk. If the assets it owns fall, the fund falls. It may also carry currency, liquidity, concentration, tracking, counterparty or structural risk, depending on what it holds and how it gains exposure.
