Yesterday afternoon, CNBC ran a segment on how investors might manage their 401(k)'s in turbulent times. With self-directed defined contribution plans supplanting traditional pensions, there's a sense in which we're all money managers now, so this stuff matters in a big way. (For our perspective on this problematic state of affairs, see this June item.)
When one of CNBC's guests suggested that the key to long-term success is to establish the right asset asset allocation and keep it that way, we nodded in agreement. But when another guest insisted that the way to do that was to sign up for automatic quarterly rebalancing, we stared in disbelief.
As we've noted elsewhere, the only advantage of calendar-driven rebalancing is that it can be automated (or, in do-it-yourself accounts, relatively automatic). In the absence of better decision rules, rebalancing once-per-period is generally better than not rebalancing at all. But two questions arise: (1) What's the right period? And (2) can we rebalance for better reasons than the mere passage of time?
First, the right period is not quarterly. By trimming all high-performing asset classes back every quarter, investors would preclude their winners from carrying their portfolios. After all, asset class outperformance tends to persist for years, not quarters.
Think of small-cap, international, and emerging market stocks, which outperformed large-cap stocks and domestic bonds for several years. Small-cap stocks have clearly underperformed in 2007, so periodic rebalancing (i.e., active risk management) is important. But cutting those positions back every quarter would have been very costly. In the context of long-term retirement accounts, the opportunity cost of foregone compounding would be enormous.
And that leads us to our second question. If quarterly rebalancing is too frequent, what better decision rules can investors use? If one must opt for a calendar-based answer, we'd suggest nothing more frequent than annual rebalancing, which is more than adequate to manage risk and less return-impairing than more frequent alternatives.
But even better than calendar-driven rebalancing is a discipline rooted in tolerance intervals, or how far you'll let an asset class deviate from its target portfolio weight before you rebalance. The idea here is simple: Rebalancing should be driven by actual developments in the capital markets, not by the arbitrary and irrelevant passage of time.
The problem with tolerance-driven rebalancing is that it takes a little work and discipline. But the likely payoffs--improved long-term performance, reduced trading expenses, and better tax efficiency, all in the context of appropriate risk management--make this alternative to the typical calendar-driven formula a clear winner.