ETF Liquidity Explained: Why Trading Volume Tells Only Half the Story

12th Oct 2026 14:51

(Sharecast News) - Knowledge Hub: ETF Liquidity Explained: Why Trading Volume Tells Only Half the Story

Liquidity is one of the most misunderstood concepts in ETF investing. Many investors assume that an ETF's liquidity can be judged simply by looking at how many shares change hands each day. At first glance, this seems perfectly logical. A heavily traded ETF should, in theory, be easier to buy and sell than one with relatively low trading volumes. Yet the ETF market does not operate in quite the same way as the ordinary equity market. While trading activity certainly matters, it represents only one layer of a much deeper liquidity ecosystem. An ETF with modest daily volume may still provide access to a vast pool of underlying liquidity, while a seemingly active product can occasionally become more difficult to trade than investors expect.

Understanding how ETF liquidity actually works is an important step in moving from ETF selection to portfolio construction. It helps investors assess transaction costs more accurately, avoid unnecessary assumptions and make more informed decisions about how different funds fit within a long-term investment strategy.

Why ETF Liquidity Is Different from Share Liquidity

When investors buy shares in a company, liquidity is largely determined by the activity taking place in that stock. If relatively few buyers and sellers exist, executing a large transaction without affecting the price can become challenging. The available liquidity is therefore tied closely to the trading activity of the shares themselves. ETFs operate under a different framework. While investors can buy and sell ETF units on an exchange throughout the trading day, the pool of liquidity extends beyond the trading volume visible on the screen. Behind the scenes sits a creation and redemption mechanism that allows market makers and authorised participants to create new ETF units or remove existing ones in response to demand.

This means an ETF's liquidity is often linked more closely to the liquidity of its underlying holdings than to the volume of ETF shares traded on any particular day. A global equity ETF may show relatively modest exchange turnover while still offering access to millions of pounds worth of liquidity through the deep underlying markets in which it invests. The result is a market structure that behaves quite differently from traditional assumptions about trading activity and market depth.

The Hidden Layer of ETF Liquidity

One of the reasons ETFs have become such an important part of modern markets is their ability to tap into liquidity that exists beyond the exchange order book. Suppose an investor wants to buy a substantial position in an ETF tracking the S&P 500. The visible supply of ETF units available for sale may initially appear limited. However, market makers can purchase the underlying shares and create additional ETF units to satisfy demand. Equally, if investors wish to sell significant positions, units can be redeemed and converted back into the underlying assets.

This creation and redemption process effectively allows liquidity to expand and contract according to market demand. Rather than being constrained solely by the number of ETF units already trading, the market can draw upon the liquidity of the securities held within the fund. For investors, this distinction is crucial because it explains why daily trading volume often provides an incomplete picture of an ETF's true liquidity profile.

Why Trading Volume Can Be Misleading

Many investors screen ETFs by assets under management and average daily trading volume. While both metrics offer useful information, neither should be viewed in isolation. A newly launched ETF may have relatively low trading activity yet track a highly liquid market such as large-cap US equities. Executing sizeable trades may still be straightforward because authorised participants can easily access the underlying securities and create additional units when necessary.

Conversely, an ETF investing in less liquid areas of the market may record healthy trading volumes while remaining dependent on underlying assets that are inherently difficult to buy and sell. In such cases, the apparent liquidity visible on the exchange may not fully reflect the liquidity risks embedded within the portfolio. The more useful question is therefore not simply how much the ETF trades, but how liquid the assets inside the ETF are. In many respects, that underlying portfolio provides the clearest indication of the liquidity available to investors.

The Importance of Bid-Offer Spreads

Liquidity is perhaps best understood through transaction costs rather than trading volume alone. One of the most visible indicators of ETF liquidity is the bid-offer spread, which represents the difference between the price at which investors can buy and the price at which they can sell. Typically, highly liquid ETFs tracking major indices exhibit relatively tight spreads because there is significant competition among market makers and abundant liquidity in the underlying securities.

Wider spreads can signal increased trading costs and may indicate a more complex underlying market. Fixed-income ETFs, specialist thematic funds and products targeting niche sectors can sometimes display wider spreads, reflecting the additional costs involved in accessing those markets. For long-term investors, spread costs may appear modest when viewed in isolation. However, they represent an immediate drag on returns and can become particularly relevant for investors making regular contributions or frequent portfolio adjustments. Assessing liquidity through spreads often provides a more practical perspective than focusing exclusively on trading volumes.

Liquidity During Market Stress

The true value of liquidity is often revealed during periods of market turbulence rather than during calm market conditions. When volatility rises sharply, investors naturally focus on whether they can trade efficiently and at fair prices. During such periods, ETF liquidity occasionally attracts scrutiny because exchange-traded prices may move more visibly than investors are accustomed to seeing.

Yet market volatility can highlight one of the ETF structure's strengths. Because ETFs continue trading throughout the day, they often provide real-time price discovery even when activity in the underlying assets becomes less frequent. This can sometimes create the impression that ETFs are less stable than their underlying holdings when, in reality, they are simply reflecting changing market expectations more rapidly. For investors, periods of market stress illustrate why liquidity should be viewed as a dynamic characteristic rather than a fixed statistic. Conditions evolve, and liquidity should be assessed with an understanding of how a fund may behave when markets are under pressure, not merely when trading conditions are benign.

Larger Doesn't Always Mean More Liquid

Assets under management are frequently used as a shorthand measure of ETF quality, with the assumption that larger funds are automatically easier to trade. Size certainly provides advantages. Larger ETFs often attract more market makers, tighter spreads and deeper institutional participation. Nevertheless, fund size alone does not determine liquidity. A relatively small ETF tracking a highly liquid benchmark may offer a superior trading experience to a larger product investing in specialist or difficult-to-access markets.

Investors should therefore be careful not to confuse popularity with liquidity. While the two often move in the same direction, they are not interchangeable concepts. Ultimately, the characteristics of the underlying assets remain one of the most important determinants of how efficiently an ETF can be traded.

What ETF Liquidity Means for Portfolio Construction

For most long-term investors, liquidity is less about making rapid trading decisions and more about ensuring flexibility when portfolio adjustments become necessary. A well-constructed portfolio should allow investors to rebalance efficiently, add to positions during market weakness and adapt asset allocations as circumstances evolve. ETFs have become widely used portfolio building blocks largely because their liquidity framework supports these objectives across a broad range of markets and asset classes.

Understanding liquidity also helps investors move beyond simplistic metrics when selecting funds. Rather than dismissing an ETF because daily volume appears low, investors can evaluate the broader ecosystem supporting the product, including the liquidity of the underlying market, the quality of market making and the efficiency of the creation and redemption process. This deeper perspective often leads to better investment decisions than relying on headline statistics alone.

The Bottom Line

ETF liquidity is often portrayed as a simple function of trading volume, but the reality is considerably more sophisticated. Unlike ordinary shares, ETFs benefit from a market structure that allows liquidity to be sourced not only from exchange trading but also from the underlying assets held within the fund. For investors, this means judging liquidity requires a broader assessment than simply looking at how many ETF shares change hands each day. Bid-offer spreads, underlying market depth, fund structure and the efficiency of authorised participants all play important roles in determining how easily a position can be bought or sold.

As investors progress from choosing individual ETFs to constructing diversified portfolios, understanding liquidity becomes increasingly valuable. It encourages a more informed assessment of trading costs, portfolio flexibility and market access, helping investors focus on what ultimately matters most: building a portfolio capable of delivering long-term investment objectives with as few avoidable frictions as possible.