ETF structure explained: how exchange-traded funds are created and redeemed

The mechanism by which ETF shares are created and redeemed is what separates exchange-traded funds from ordinary mutual funds—and what explains their pricing accuracy, cost efficiency, and tax treatment. ETF structure rests on a process mediated by large financial intermediaries called authorised participants, and understanding it clarifies why ETFs can be as cheap and tax-efficient as they are.

What ETF structure is

An ETF is a fund that holds a basket of underlying assets and issues shares that trade on a stock exchange throughout the day. Unlike a mutual fund, which can only be bought and sold at the single price calculated at market close each day, an ETF's shares trade continuously at market prices during exchange hours.

The structural distinction that makes this possible is the creation and redemption mechanism. Retail investors buy and sell ETF shares on the secondary market—between each other, via a broker. The fund itself does not deal directly with retail investors. Instead, it works exclusively with a small number of large financial institutions called authorised participants (APs), typically major banks or broker-dealers who hold contractual agreements with the ETF issuer.

How it works

When demand for ETF shares rises and the ETF's market price climbs above the value of its underlying holdings—known as the net asset value, or NAV—an authorised participant can profit by creating new ETF shares. The AP assembles a basket of the ETF's underlying securities, matching the fund's holdings in the required proportions, and delivers this creation basket to the ETF issuer. In exchange, the issuer delivers a large block of new ETF shares—typically 25,000 to 100,000 shares per creation unit, depending on the fund. The AP then sells these shares on the exchange.

Redemption is the reverse. When ETF shares trade at a discount to NAV, an AP can buy ETF shares cheaply on the market, accumulate enough to form a redemption unit, and exchange them with the ETF issuer for the underlying basket of securities. The AP then sells those securities in the market at full value, capturing the discount as profit.

This arbitrage process—creation when the ETF trades at a premium, redemption when it trades at a discount—is self-correcting. It keeps the ETF price closely aligned with NAV without requiring any intervention from the fund manager or retail investors.

The exchange between APs and the ETF issuer is an in-kind transaction: securities move in, ETF shares move out (creation), or ETF shares move in, securities move out (redemption). No cash changes hands between the AP and the fund. This is what gives ETFs much of their tax efficiency: because the fund does not sell securities to raise cash for redemptions, it does not realise capital gains that would otherwise be distributed to remaining shareholders. Traditional mutual fund redemptions require the fund to sell holdings, which can trigger capital gains distributions that all remaining shareholders must pay tax on, even if they did not sell their own shares.

What the evidence shows

Research on ETF pricing consistently confirms that the creation and redemption mechanism keeps premiums and discounts narrow for ETFs tracking liquid, transparent markets. For large-cap equity ETFs, the average daily premium or discount is typically less than five basis points under normal conditions. The mechanism works because the arbitrage opportunity is immediately visible—any deviation between the ETF price and the NAV of its published holdings can be acted on in real time by APs with the infrastructure to do so at scale.

The mechanism shows its limits when the underlying market is less liquid than the ETF itself. During the market disruption in March 2020, certain bond ETFs experienced premiums and discounts that temporarily widened to several percentage points. The ETF continued trading freely on the exchange while the underlying bond market experienced acute illiquidity—APs could not readily assemble or dispose of the underlying bond baskets at reasonable cost, so the arbitrage that normally compresses premiums and discounts could not operate efficiently. In this sense, bond ETF prices during that period were arguably more informative about current market conditions than the stale NAV calculations based on illiquid bonds.

Limitations and trade-offs

The in-kind creation and redemption mechanism functions smoothly when the underlying assets are liquid and the holdings are transparent. For ETFs tracking less liquid markets—small-cap equities in frontier markets, high-yield corporate bonds, or commodities held in physical form—APs face higher costs and risks in assembling the creation basket. These costs are ultimately reflected in wider bid-ask spreads on the ETF and in larger, more persistent premiums or discounts.

Not all ETFs use in-kind creation and redemption. Some ETFs, particularly those using derivatives or tracking international markets with settlement timing differences, use cash creation. In a cash creation process, the AP delivers cash rather than the underlying securities, and the fund manager constructs the portfolio directly. Cash creation is more operationally flexible but less tax-efficient, since the manager must buy and sell securities for cash. Investors in cash-creation ETFs bear slightly different structural risks from those in standard in-kind ETFs.

ETF structure in pfolio

pfolio uses ETFs as the primary instrument for multi-asset portfolio construction, and the creation and redemption efficiency of those ETFs is directly relevant to portfolio cost and tracking quality. ETFs available for use in pfolio portfolios are listed in the Assets section, with their asset class and type classifications visible alongside. ETF performance data and exposure details are available in pfolio Insights.

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