In my last post, I discussed ETF liquidity risk. After the post, a subscriber to ETFMathGuy asked me to talk more about this risk and how it relates to the wide variety of commission-free ETFs now available.
Bid-ask Spreads
Bid-ask spreads are an excellent way to measure liquidity. Less liquid ETFs generally have higher bid-ask spreads. But, the liquidity of the securities held by the ETF also affects bid-ask spreads. The image below shows the distribution of bid-ask spreads for Fidelity commission-free ETFs, which I updated from my April 2019 post.
Minimizing costs
As we see from these results, there is a wide variation of bid-ask spreads. So, about half have spreads under 0.1%, and about 80% under 0.3%. For ETFs traded commission-free, these spreads are likely the largest contributor to cost of ownership. To reduce this cost, an investor can either buy-and-hold for extended periods, or choose ETFs with lower bid-ask spreads. Investors should also avoid trading ETFs close to the market open and close. Higher volatility over a typical trading day can often occur close to the market’s open and close, and can produce higher bid-ask spreads.
What about ETF liquidity during high market volatility?
It is very likely that, during periods of high market volatility, bid-ask spreads will grow. This growth is simply the result of finding a balance between supply and demand. Or, in the case of ETFs, this balance occurs when an ETF seller finds a buyer. Remember that, due to liquidity risk, we can expect a return premium over risk-free investments. If market volatility is a concern, investors should seek lower volatility investments (e.g. bonds over stocks), and/or seek lower volatility in their portfolio through diversification.
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