Rebalancing plays a crucial role in ongoing portfolio management, both to ensure that the overall risk of the portfolio doesn’t drift higher (as risky investments can outcompound the conservative ones in the long run), and to potentially take advantage of sell-high buy-low opportunities. The caveat: it’s not entirely clear how often a portfolio should be rebalanced, in order to achieve these goals.
The conventional wisdom is to rebalance a portfolio at least once per year, and possibly even more frequently, such as quarterly or monthly. A deeper look, however, reveals that more frequent rebalancing will on average have little impact on risk reduction, even less benefit from a return perspective, and just racks up unnecessary transaction costs along the way.
Instead, the research suggests a superior rebalancing methodology is to allow portfolio allocations to drift slightly, and trigger a rebalancing trade only if a target threshold is reached. If the investments grow in line and the relative weightings don’t change, no rebalancing trade occurs. However, if these “rebalancing tolerance bands” are breached, the investment – and only the investment – that crosses the line, is then bought or sold to bring it back within the bands.
The one caveat to the process of tolerance band rebalancing is that it requires ongoing active monitoring of the portfolio itself, to ensure that you know when a threshold has been reached. Fortunately, though, a growing number of rebalancing software tools are available to help advisors track each investment, its rebalancing thresholds, and even automatically calculate and queue up the rebalancing trades necessary to bring the portfolio in line again!