U.S. fixed income ETF assets under management (AUM) stood at almost $1.2 trillion as of June 2022, more than double their footprint of five years ago. The second quarter saw inflows of $46 billion as investors continued to adopt bond ETFs even as bond prices were falling amid the biggest spike in inflation in 40 years.¹ The accelerating growth in assets has been accompanied by increasing trading volumes, as the chart below shows.

Interest in bond ETFs has grown for similar reasons to those driving interest in ETFs overall in recent years: generally lower costs, efficient implementation of diversification, flexibility tied to their tradability, and tax efficiency.

But bond ETFs differ from equity ETFs in a few distinct areas that investors should be aware of. 

Equity and fixed income markets are structured in fundamentally different ways. Whereas equities are traded on public exchanges and have real-time transparency into intraday pricing, individual bonds trade over the counter and can lack pricing transparency.² The challenges of getting optimal execution in fixed income markets are exacerbated by the fragmented structure of underlying markets.

In other words, the over-the-counter trading makes it challenging for bond dealers and asset managers to pin down the sourcing of bonds and determine their fair-value prices. For this reason, it’s also more challenging to construct fixed income products. This makes it important to evaluate an ETF issuer on its fixed income trading expertise.

Vanguard’s approach and large footprint enable operational efficiency and, on a relative basis, a larger number of bonds in its portfolios, allowing for greater coverage across most markets. Additionally, Vanguard’s strong reputation with other market participants provides access to favorable new-deal allocations, best possible execution from bond dealers, and participation in primary issuances.

Unlike most index equity ETFs, which often replicate their benchmarks with great precision, most fixed income products sample their benchmarks heavily. This allows them to avoid the cost and impracticality of full replication in the relatively opaque bond markets. Sampling is important in larger or less liquid parts of the market, such as international fixed income, emerging-market bonds, and corporate credit.

Because of the sampling that prevails in fixed income, it’s imperative that asset managers have well-staffed and experienced fixed income teams and a time-tested, sophisticated process. Vanguard, for example, has a dedicated team of credit researchers and traders focusing on matching key benchmark characteristics such as duration, subsector weights, credit quality, and issuer exposure, all in the pursuit of optimal tracking. Our fully integrated but independent risk management group ensures that we balance tight tracking with mitigation of transaction costs.

For both equity and fixed income ETFs, the quoted market price of each ETF is typically displayed as the midpoint of its bid and ask, which reflects the bid and ask prices of the underlying securities. An equity ETF’s end-of-day net asset value (NAV) will then be based on the closing prices of the underlying securities.

For a bond ETF, however, the NAV is struck using the bid-side pricing of the underlying securities, as the chart below shows. That lower NAV means that bond ETFs typically close at a premium on a daily basis.

Because all bond ETFs are priced this way and all bonds exhibit this bid-side pricing as a matter of course, it’s critical to evaluate the consistency of the premium in a given ETF, not just its mere existence, as you seek to determine fair value of a given bond ETF.

Put differently, if a fixed income ETF is trading at a premium, investors might be concerned about a potential “baked in” loss upon sale. However, if the premium is consistent, the risk of that baked-in loss is mitigated.

Although bond ETFs are potentially a lower-tax way to own fixed income compared with owning individual bonds, investors should consider asset location—the type of account the assets are held in—because tax consequences can be distinct with bond ETFs. Bond ETF income will come primarily in the form of dividends, but investors should be aware that bond ETFs can also generate capital gains.  

Most bond ETFs seek to maintain a specific maturity over time. This means that as bonds roll in and out of the specified maturity bands, portfolio managers must buy and sell to maintain effective tracking. This naturally occurring process can lead to capital gains. Although fixed income ETFs are generally more tax efficient than active fixed income strategies, the ETFs may still pay out capital gains because of their structure.