What caught my eye this week.
Two diligent bloggers took a run at the subject of rebalancing portfolios this week.
First up – in a tour de force that could give our own @TA a run for his carefully husbanded money – Occam Investing dove deep into the fabled ‘rebalancing bonus’, where investors see extra returns from regularly rejigging their asset allocation.
The post concludes that while such a rebalancing windfall is obviously welcome, the bonus cannot be banked on in the real-world:
Am I personally likely to benefit from the rebalancing bonus over the long term?
Probably not.
I’m not confident it’s possible to forecast anything with a great level of accuracy in markets, let alone being able to predict correlations, returns, and volatility. I’m certainly not confident enough to start making my portfolio more complicated by splitting it up, and therefore increasing trading costs, time required for monitoring, and risk of tinkering.
I may be sacrificing a potential rebalancing bonus by investing in a global tracker because I can’t rebalance its constituent parts.
But in my view, the benefits of a global tracker are worth it.
Not so well endowed
Funnily enough, this very same week on a A Wealth of Common Sense, Ben Carlson spotted the rebalancing bonus roaming in the wild.
After showing how a simple portfolio of index-tracking ETFs would have beaten the returns of a bunch of sophisticated endowment funds over the past decade, Ben noticed that an investor with an 80/20 stock/bond split across three particular Vanguard tracker funds could have conjured up even higher returns by annually rebalancing:
If you were to simply multiply the weights for the 80/20 portfolio (48% U.S. stocks, 32% int’l stocks, 20% bonds) by [their] returns you would get an overall annual return of 8.9%.
But the actual 10 year annual return for the 80/20 portfolio shows 9.1%.
How could this be?
The difference here is the rebalancing bonus.
Both authors show their workings, and both are well worth a read.
Everything in moderation
While any investor would take bonus returns where they can get them, rebalancing is best thought of as a risk management tool rather than a source of alpha.
You may or may not see a rebalancing bonus in your years as an investor. That’s down to the luck of the historical draw.
But you might well expect to have a lower-risk portfolio if you keep your allocations broadly in-line with where you’ve determined they should be.
As a naughty active investor, my portfolio is to a passive 60/40 set-up what quantum mechanics is to Newtonian physics. Investments pop in and out of existence in my portfolio all the time. Any one of them could affect my returns (for good or ill) much more than the modest impact of annually rebalancing between asset classes.
Nevertheless, these days I too try to ensure nothing grows too far out of whack. This can mean trimming winning positions, which I do knowing full well this can be a behavioural bias and mathematical blunder that curbs long-term returns.
So why do it?
Because you never really see a catastrophic blow-up in investing that doesn’t involve over-exposure to a share, sector, geography, or asset class.
Stay vaguely diversified and the worst you will likely do is relatively poorly.
Of course we all hope to do better than that! But avoiding disaster is the number one rule.
As Warren Buffett’s sidekick Charlie Munger says: “All I want to know is where I’m going to die, so I’ll never go there.”
Amen to that!




