ExplainersAdvanced· 7 min read

How an ETF is actually created

The one thing to remember

Arbitrage, not good intentions, is what keeps an ETF's price glued to the value of its holdings.

The question

Understand why an ETF tracks its index so tightly, and when that machinery can fail.

Figure

The same argument as the text, as a chain. Each step is what makes the next one possible.

Figure

Not virtue, arbitrage. If the wrapper drifts from the contents, an institution swaps one for the other and pockets the gap, which closes the gap.

1
An ETF is a wrapper around a basket
It holds the underlying shares. Its net asset value is simply what those shares are worth. The ETF's own share price, though, is set by supply and demand in the market, and there is no law of nature keeping the two together.
2
Large institutions can swap the wrapper for the contents
Authorised participants can hand the fund a basket of the underlying shares and receive new ETF units, or hand back units and receive the shares. This is creation and redemption, and it happens in enormous blocks.
3
Which makes any gap a free lunch, so the gap closes
If the ETF trades above the value of its holdings, an institution buys the shares, creates units, sells them, and pockets the difference. Doing so pushes the price back down. The discipline is not virtue, it is arbitrage, which is far more reliable.
4
And it strains when the underlying stops trading
If the ETF holds illiquid bonds that nobody is pricing, the arbitrage cannot run, and the ETF can trade at a meaningful discount to a net asset value that is itself now fictional. This is where the mechanism creaks.
The plumbing is superb for liquid equities and much more fragile for exotic underlyings. Know which one you own.

Try it

Compound interest simulatorInteractive

Compounding Without compounding

Starting amount1000 £

Added each month200 £

Annual return7%

Years30

You put in

£73,000

Growth

£179,111

Final

£252,111

Drag the years slider. Notice the curve barely lifts for a decade, then goes near vertical. That is why starting early matters more than the rate.

You have got it when

You can explain why an equity ETF almost never drifts from its index, without using the word 'trust'.

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