What is an ETF and how does it work? Complete guide

An ETF (Exchange Traded Fund) is an investment fund that trades on the stock exchange and is bought and sold like a share. It combines the diversification of a fund with the flexibility of trading in real time and very low costs. In this guide we explain what an ETF is, how it works, its advantages and drawbacks, and the tax detail that, in Spain, makes all the difference compared with a traditional investment fund.

What is an ETF and how does it work?

An ETF, or exchange-traded fund, is a hybrid between an investment fund and a share. On the inside it is a fund: a basket of assets (shares, bonds, commodities) run by a fund management company and held by a depositary, with your money kept separate from both balance sheets. On the outside it behaves like a share: it trades on the stock exchange throughout the session and you can buy or sell it in seconds through your broker.

Here is the first big difference from traditional funds: a fund calculates its net asset value once a day, at the close, while an ETF's price moves in real time with the market and you know exactly what you are paying the moment you place the order.

The vast majority of ETFs are index funds: they do not try to beat the market, but to replicate an index as faithfully and cheaply as possible. There are ETFs on equity indices such as the S&P 500, on bonds, sectors, countries, commodities and even volatility. Today the range covers virtually any market you can imagine.

A bit of history: from the “Spider” to a giant market

The first modern ETF was born in January 1993: the SPDR S&P 500, known as “The Spider” and managed by State Street Global Advisors. From 1996, iShares burst onto the scene with international ETFs and opened a race between fund managers that Barclays, BlackRock and, later, Vanguard would join. Three decades on, ETFs channel trillions of euros worldwide and are the gateway to index investing for millions of savers.

Advantages of investing in ETFs

• Very low costs: the total expense ratio (TER) of index ETFs typically ranges between 0.05% and 0.40% per year, compared with the 1.5%-2% common in many actively managed funds.
• Instant diversification: with a single purchase you gain exposure to hundreds or thousands of securities, countries or currencies.
• Liquidity and flexibility: they trade on the stock exchange at any point in the session, with a price you know instantly.
• Transparency: they publish their holdings, price and trading volume daily.
• Accessibility: they let you invest small amounts in markets that used to be hard for retail investors to reach.

Drawbacks of ETFs

• Trading costs: every trade goes through the exchange, so you pay your broker's fee plus the gap between the buying and selling price (the spread).
• Less tax-efficient in Spain: ETFs do not benefit from the tax-free transfer regime (traspasos) enjoyed by traditional funds. This is the most important point and we cover it in detail in the next section.
• Temptation to overtrade: being able to buy and sell in real time invites impulsive moves that rarely help the long-term investor.
• Currency risk: many ETFs invest in assets denominated in dollars or other currencies, and those swings affect your returns in euros unless the product is hedged.

The key tax point in Spain: ETFs do not allow tax-free transfers

In Spain, traditional investment funds enjoy a unique advantage: the transfer regime (traspasos) under art. 94 LIRPF (Spanish income tax law). You can move your money from one fund to another without selling, without crystallising gains and, therefore, without paying tax at that point. ETFs, although legally funds, fall outside this regime because they are exchange-traded: every switch between ETFs means selling and buying, and every sale at a gain is taxed.

Let's look at an example in euros. Imagine you invested €20,000 and your position is worth €30,000 today. You want to change products because your strategy has evolved:

• With a transferable index fund: you order the transfer, pay no tax at that point, and the full €30,000 stays invested and generating returns.
• With an ETF: you sell, crystallise a €10,000 gain and pay tax in the Spanish savings tax base, at rates from 19% to 30% depending on your bracket. At the 19% rate, you would pay around €1,900 that leaves your portfolio for good.

Be aware: the fund does not free you from taxes, it defers them. You will pay tax when you finally redeem. But that deferral lets the money you would have handed to the tax authority keep compounding in your favour for years, which is decisive in portfolios that are rebalanced frequently. You will find the full detail in our guide on the taxation of investment funds.

ETF or traditional index fund? Comparison

As a general rule: if you make regular contributions, rebalance or expect to change strategy, the transferable index fund is usually more tax-efficient in Spain. If you want real-time pricing, a very specific exposure or minimal costs on a position you do not plan to touch, the ETF scores points. They are not mutually exclusive: many portfolios combine both.

What types of ETF exist

By replication method

Physical replication ETFs buy the index constituents directly. Synthetic replication ETFs obtain the index return through a derivative with a counterparty, which adds an extra layer of risk in exchange, at times, for better replication of certain markets.

By what they do with dividends

Accumulating ETFs automatically reinvest dividends within the fund. Distributing ETFs pay them out to you periodically; in that case they carry a 19% withholding at source and are taxed each year in your Spanish savings tax base.

By the asset they track

There are global and regional equity ETFs, fixed income ETFs, and sector and thematic ETFs. Exchange-traded products on commodities are usually actually ETCs, a different legal structure with risks of its own: we explain it in our guide ETF vs ETC. And if you want to see how exchange-traded funds on the world's most-followed index compare, take a look at our analysis of the best S&P 500 ETFs.

How we approach this at Quality Finance

At Quality Finance Wealth Management we work with open architecture: we analyse funds and ETFs from multiple external fund managers and select the vehicles that best fit each client's wealth, weighing costs, taxation, liquidity and your time horizon. The choice between an ETF and a transferable fund is never generic: it depends on how much you invest, how you contribute and what changes you expect to make. If you would like to review how these vehicles could fit into your portfolio, we would be delighted to talk.

Frequently asked questions

What is the difference between an ETF and an index fund?

Both usually track an index, but an ETF trades on the stock exchange with real-time pricing, while a fund is subscribed and redeemed at a daily net asset value. In Spain, on top of that, traditional funds allow tax-free transfers (traspasos) and ETFs do not.

How are ETFs taxed in Spain?

When you sell at a profit, the gain is taxed in the Spanish savings tax base, at rates from 19% to 30% depending on your bracket. Dividends paid by distributing ETFs carry a 19% withholding at source.

Can you switch ETFs without paying tax?

No. The transfer regime under art. 94 LIRPF applies to traditional investment funds and excludes ETFs because they are exchange-traded. Switching ETFs means selling, paying tax on the gain and buying again.

How much money do I need to invest in an ETF?

The minimum is the price of one unit, which in many cases sits between €10 and €500. Remember to add your broker's trading fee, which hits very small contributions especially hard.