November 01, 2022
There are risks in letting your asset allocation drift too far from your target—including ending up with more risk in your portfolio than you signed up for. At the same time, there are taxes and trading costs associated with rebalancing. In a recent paper, Vanguard investment strategists analyzed approaches to portfolio rebalancing and how it can be optimized.
The Vanguard team examined three methods often employed by investors, advisors, and asset managers for rebalancing portfolios:
Our strategists employed a framework for determining an ideal risk-return and cost-efficient rebalancing strategy. You can learn more about the methodology in the research paper. It requires forecasting a distribution of asset returns (an entire range of returns rather than a single-point forecast) and transaction costs, which are critical in assessing the impact of rebalancing on portfolio wealth after transaction costs are taken into account.
For investors who don’t participate in tax-loss harvesting or who are not concerned with maintaining tight tracking to a multiasset benchmark portfolio, rebalancing a portfolio on an annual basis was the best method in terms of the risk-return trade-offs. It is optimal largely because it allows investors to harvest the equity risk premium while also generating lower transaction costs than more frequent rebalancing.
Notes: Results are based on simulations from the forecasting framework and maximization of post-transaction-cost wealth for various portfolios and rebalancing strategies shown above. The CFE (certainty fee equivalent) is the benefit of selecting the optimal rebalancing strategy relative to another rebalancing method or, conversely, the fee an investor would be willing to pay relative to another rebalancing method. “Bps” equals basis points; a basis point is one-hundredth of a percentage point. U.S. bonds are represented by the Bloomberg U.S. Aggregate Bond Index, non-U.S. bonds by the Bloomberg Global Aggregate ex-U.S. Index, U.S. equities by the MSCI US Broad Market Index, and non-U.S. equities by the MSCI All Country World Index ex USA. Data are as of June 2022.
While stock market declines like the one we’ve experienced this year may tempt investors to rebalance more frequently, our research indicates that less-frequent rebalancing is efficient even during periods of market turmoil. Transaction costs tend to rise during volatile environments, which makes rebalancing expensive. Moreover, an investor may rebalance in one direction and then have to reverse the transaction because the market whipsawed the opposite way, which can happen during periods of turmoil.
Our research shows that optimal rebalancing methods are neither too frequent, such as monthly or quarterly calendar-based methods, nor too infrequent, such as rebalancing only every two years. For many investors, implementing an annual rebalancing is optimal.
All investing is subject to risk, including the possible loss of the money you invest. Be aware that fluctuations in the financial markets and other factors may cause declines in the value of your account. There is no guarantee that any particular asset allocation or mix of funds will meet your investment objectives or provide you with a given level of income.
Investments in bonds are subject to interest rate, credit, and inflation risk.