How ETF Arbitrage Works

Traders, especially high-frequency traders, can take advantage of mispricings in the market, even if these inefficiencies last for just a few minutes or seconds. Mispricing can occur between two similar securities, like two S&P 500 ETFs, or within a single security, where the trading value differs from the net asset value (NAV).

Market participants can exploit both types of inefficiencies through arbitrage. Taking advantage of arbitrage opportunities usually involves buying an asset when it is underpriced or trading at a discount and selling an asset that is overpriced or trading at a premium.

Exchange-traded funds (ETFs) are one such asset that can be arbitraged. ETFs are securities that track an index, commodity, bond, or basket of assets like an index fund, similar to mutual funds. But unlike mutual funds, ETFs trade just like a stock on a market exchange. Therefore, throughout the day, ETF prices fluctuate as traders buy and sell shares. These trades provide liquidity in ETFs and transparency in price. Still, they also subject ETFs to intraday mispricing, as the trading value can deviate, even slightly, from the underlying net asset value. Traders can then take advantage of these opportunities.

ETF Arbitrage: Creation and Redemption

ETF arbitrage can occur in a couple of different ways. The most common way is through the creation and redemption mechanism. When an ETF issuer wants to create a new ETF or sell more shares of an existing ETF, he contacts an authorized participant (AP), a large financial institution that is a market maker or specialist. 

The AP’s job is to buy securities in equivalent proportions to mimic the index the ETF firm is trying to mimic, and give those securities to the ETF firm. In exchange for the underlying securities, the AP receives shares of the ETF. This process is done at the net asset value of the securities, not the market value of the ETF, so there is no mispricing. The reverse is done during the redemption process.

The arbitrage opportunity happens when demand for the ETF increases or decreases the market price, or when liquidity concerns cause investors to redeem or demand the creation of additional ETF shares. At these times, price fluctuations between the ETF and its underlying assets cause mispricings. The NAV of the underlying portfolio is updated every 15 seconds during the trading day, so if an ETF is trading at a discount to NAV, a company can purchase shares of the ETF and then turn around and sell it at NAV and vice versa if it is trading at a premium.

For example, when ETF A is in high demand, its price rises above its NAV. At this point, the AP will notice the ETF is overpriced or trading at a premium. It will then sell the ETF shares it received during creation and make a spread between the cost of the assets it bought for the ETF issuer and the selling price from the ETF shares. It may also go into the market and buy the underlying shares that compose the ETF directly at lower prices, sell ETF shares on the open market at a higher price, and capture the spread.

While non-institutional market participants are not large enough to play a part in the creation or redemption processes, individuals can still partake in ETF arbitrage. When ETF A is selling at a premium (or discount), individuals can buy (or sell short) the underlying securities in the same proportions and sell short (or buy) the ETF. However, liquidity may be a limiting factor, impacting the ability to engage in this arbitrage.

ETF Arbitrage: Pair Trades

Another ETF arbitrage strategy focuses on taking a long position in one ETF while simultaneously taking a short position in a similar ETF. This is called pairs trading, and it can lead to an arbitrage opportunity when the price of one ETF is at a discount to another similar ETF. 

For example, there are several S&P 500 ETFs. Each of these ETFs should track the underlying index (the S&P 500) very closely, but at any given point, the intraday prices can diverge. Market participants can take advantage of this divergence by buying the underpriced ETF and selling the overpriced one. These arbitrage opportunities, like the previous examples, close rapidly, so arbitrageurs need to recognize the inefficiency and act quickly. This type of arbitrage tends to work best on ETFs with the same underlying index.

How Does Arbitrage Impact ETF Pricing?

ETF arbitrage is thought to aid the market by bringing the market price of ETFs back in line with NAV when divergence happens. However, questions related to whether ETF arbitrage increases market volatility have arisen. A 2018 study titled “Do ETFs Increase Volatility?” by economists Ben-David, Franzoni, and Moussawi, examined the impact of ETF arbitrage on the volatility of the underlying securities. They concluded that ETFs can actually increase daily volatility of the underlying stock by up to 3.4%. 

Other questions remain about the extent to which mispricings can occur between the ETF and underlying securities when markets experience extreme moves, and whether the benefit from the arbitrage, which causes NAV and market price to converge, may fail during extreme market moves. For example, during the flash crash in 2010, ETFs made up many of the securities that saw big price declines that also corresponded with large mispricings that were unhinged from the NAVs of their underlying indexes.

The Bottom Line

ETF arbitrage is not a long-term strategy. Mispricings happen in the short term, and these opportunities close within minutes, if not sooner. But ETF arbitrage is advantageous for the arbitrageur and the market. The arbitrageur can capture the spread profit while driving the ETF’s market price back in line with its NAV as the arbitrage closes.

Despite these market advantages, research has shown that ETF arbitrage may increase the volatility of the underlying assets as the arbitrage emphasizes or intensifies the mispricing. The perceived increase in volatility needs further research. In the meantime, market participants will continue to benefit from temporary spreads between share price and NAV.