How often should I rebalance?

I was originally going to write this post on how to maximize returns through rebalancing.  My underlying assumption was that rebalancing helps your portfolio by “buying low and selling high,” and that I only needed to figure out the best rebalancing interval (monthly, yearly, etc.) that would maximize my returns. Through my research, however, I was able to have some sense knocked into me by a couple of enlightening articles, and one fantastic quote by a Vanguard research report “Best Practices for Portfolio Rebalancing”  July, 2010:

“It is important to recognize that the goal of portfolio rebalancing is to minimize risk (tracking error) relative to a target asset allocation, rather than to maximize returns.”

This was such a great reminder for me.  The whole point of rebalancing is to make sure your portfolio reflects the level of risk that you are comfortable with.  If at the outset, you say you want 60% stocks and 40% bonds, then even a slight 0.1% shift towards stocks means your portfolio has more risk than you want it to.  Rebalancing for any other reason than to minimize tracking error is a form of active trading, which by now, it should be pretty clear I am against.

Should I rebalance every day then? Theoretically, Yes.  In reality, No.  In reality, it usually costs money to make trades.  Even if it doesn’t (like if you have a Schwab account and only buy Schwab ETFs), making these trades takes time.  So the real question is how much tracking error are you willing to accept in your portfolio, and how much time are you willing to take to maintain it.

How often should I rebalance in reality?  The industry standard is to rebalance every year, and that is a perfectly good approach.  In the Vanguard report linked above, Vanguard has a slightly more nuanced approach that I think makes the most sense.  The report suggests that you monitor your portfolio semi-annually or annually, and only rebalance when an asset drifts more than 5% from its target percentage.  They go on to say that this approach “is likely to produce a reasonable balance between risk control and cost minimization for most investors. Annual rebalancing is likely to be preferred when taxes or substantial time/costs are involved.”

I would also suggest that you rebalance every time you add money to your account. Recently I’ve been putting money into a “house downpayment” account where I buy a number of index funds.  Since this is the type of account that I don’t make automatic deposits from my paycheck every month, I usually wait a few months and make a large contribution to portfolio and use the contribution to buy more shares of the 5 different ETFs that make up the portfolio.   Since I have to place orders anyway, I might as well make sure that my portfolio will reflect my preferred asset allocation after I finish the new trades.  This is an easy way to rebalance more than just once a year without requiring extra effort.

Does rebalancing help you get higher returns?  Ok, lets say you agree to the basic premise that rebalancing is only for the purpose of minimizing tracking error.  But does rebalancing actually get higher returns?  Is there is a rebalancing time interval (or threshold) that historically offers the best returns?  If so, then you would want to know, right?  The  answer  unfortunately depends on who you ask.

In the Vanguard study (mentioned twice and linked above), the summary states that, “Our findings indicate that there is no optimal frequency or threshold when selecting a rebalancing strategy. This paper demonstrates that the risk-adjusted returns are not meaningfully different whether a portfolio is rebalanced monthly, quarterly, or annually; however, the number of rebalancing events and resulting costs (taxes, time, and labor) increase significantly.”

Another financial advisor explains it in a different way.  The author says that when rebalancing, you are just as likely to “buy high and sell low” as it is the other way around.  He says that rebalancing can increase your returns – but only if you get the timing right.  In other words, you either have to be lucky, or trying your hand at market timing, which from my perspective is a losing proposition.  Two great posts explaining this can be found here and here.

Other researchers have tried to empirically prove that a certain method of rebalancing can increase returns, like this study by a Managing Director at TD Ameritrade. This study shows that there are “significant advantages of opportunistic rebalancing (look frequently and rebalance only when you need to) over traditional annual or quarterly rebalancing.”  In this approach, there is a complex method to determine whether you should initiate a rebalancing.  The approach outlined in the study is time consuming (it requires frequent portfolio checking) and borders on being an active trading strategy, but at least makes for an interesting read.

These three different takes are by no means an exhaustive inventory of all the views on rebalancing, but I think they are representative of the types of research you will find.  While you might find a complex method of rebalancing that can add a few basis points on your annual return, don’t forget that the point of rebalancing is simply to reduce your risk.