Rebalancing - the other "free lunch" in investing.
Rebalancing is probably the least understood portfolio investment tool, at least for the typical retail investor. Simply put, rebalancing means checking your portfolio after significant moves, or at regular time intervals (e.g. quarterly, half-yearly, or annually) and re-adjusting the % allocations so that they go back to the original portfolio target allocations.
For example, take a simple 70% S&P, 30% bond allocation. If you had this on in 1992, then by early 2000 the great outperformance of the S&P 500 would have meant that you had almost all your assets in stocks. I haven't checked the exact figures, but you might have 90% of assets in stocks and 10% in bonds, after the 8 year raging bull market. This is clearly way riskier than your original target of 70% stocks and 30% bonds. Varying asset performance has meant that your original allocation drifts far from your intended mix of risk and reward.
Thus, rebalancing is necessary to keep your portfolio on track. Each year (or 6 months, or 3, or whenever there's a big move), you need to see where your allocations have "drifted" to, then rebalance to get them back on target. For example, in the above case, you would sell 20% of your portfolio that is in stocks, and put that 20% back into bonds, to get back to the 70% stocks 30% bonds weighting. Obviously you would do it way more than once every 8 years
So - rebalancing is necessary to keep your portfolio at the target asset weightings, and target risk/reward levels. However, there is also a hidden benefit to rebalancing. Without going too much into the maths & theory, rebalancing can provide profits from market volatility. To use an extreme example, imagine a 50/50 stock/bond split. Let's say stocks rise 100% in 1 year, then fall 50%, to end where they started. Bonds fall 20% in year 1 and rise 25% in year 2, to get back where they started. What would be the effect of a rebalance at the end of year 1?
Asset Year 0 Year 1 Rebalance Year 2
Stocks: 50k 100k 70k 35k
Bonds: 50k 40k 70k 87.5k
Mix: 50/50 71/29 50/50 29/71
TOTAL: 100k 140k 140k 122.5k
Drawdown: 0k 0k 17.5k
Now the same if you don't rebalance
Year 0 Year 1 Year 2
Stocks: 50k 100k 50k
Bonds: 50k 40k 50k
TOTAL: 100k 140k 100k
Drawdown: 0k 0k 40k
The rebalanced portfolio gains 22.5%, compared to a 0% gain for the unrebalanced portfolio. The drawdown is 17.5k rather than 40k. By selling high and buying low, taking advantage of the huge volatility, rebalancing here adds returns whilst lowering drawdowns. Rebalancing in the midst of the volatility managed to generate a 22.5% return, despite both markets returning 0% over the 2 year period! Now, imagine using that method during the 1997-2003 boom/bust period in US stocks. You would have been booking profits on stocks in 1998, 1999, 2000, and buying into weakness in 2001, 2002, 2003. The markets were virtually net flat over that 6 year period, but rebalancing would have generated some extra returns by effectively dollar-cost averaging - buying less at high prices, selling more; and vice versa when prices fell. Not bad eh?
Obviously I have used a huge volatility move here to make it easier to see the effect. In real markets, swings will be lower, but all that means is that rebalancing adds profits and reduces drawdowns - just at more modest amounts.
To take a real-world example, I read a study which showed during the 1990s a rebalanced stock/bond portfolio would have added about 0.7% per annum to returns compared to an unrebalanced stock/bond portfolio, whilst having lower risk over the same period. Without rebalancing, the bull market in stocks resulted in a big drift to a stock-heavy portfolio, right as the bubble reached its peak. You would be overweight stocks at precisely the wrong moment.
Rebalancing is the portfolio investors secret weapon - it keeps asset allocations on target, smooths results, and boosts long-run returns whilst reducing short and long-term risk. What's not to like?
Transactions costs and tax considerations mean you should not rebalance all the time. But ideally you should do it at least once per year. In addition, whenever one asset class has had a big move and/or starts to look overvalued, rebalancing is the perfect way to exploit the possible market overshoot - book profits and ploughing them back into the cheaper alternatives. It's the perfect way to satisfy your urge for "action", allowing you to fade extreme moves without taking the risk of making an outright bet. If you were long stocks in 1999 and early 2000, rebalancing into bonds and REITS would have been a great move. Ditto going from bonds to stocks in 1998 or 2003. Regular rebalancing ensures that you sell tops and buy bottoms with regularity.