This is a guest post from Robert Brokamp of The Motley Fool. Robert is a Certified Financial Planner and the adviser for The Motley Fool’s Rule Your Retirement service. He also has a newly reinvigorated blog, and you can have your day interrupted once or twice by his Twittering. Robert contributes one new article to Get Rich Slowly every two weeks.

How would you like $4,290,387? It’s easy! Just go back to 1972 and invest $100,000 into a well-diversified portfolio. Not enough money for you? Well, then, here’s how you can add $334,124 to that tidy sum: Simply rebalance this well-diversified portfolio annually.

Okay, despite my fondness for Marty McFly, there’s no way to travel back 38 years and open a brokerage account. But the past few decades may provide clues about the next few, especially regarding portfolio behavior and the value of rebalancing. Below, we’ll look at three common beliefs about rebalancing and explain whether they’re true or false — and why.

Reduce, Reuse … Rebalance?
In case you’re new to the concept, rebalancing is the process of returning a portfolio to an investor’s predetermined appropriate allocation (for example, 65% stocks and 35% bonds). A balanced portfolio is key to ensuring steady, growing returns, but the movement of various investments over time can cause that initial, balanced allocation to change; assets that have done well become a bigger piece of the pie, while the laggards shrink to a smaller portion.

Historically, broad asset classes tend to (but don’t always) revert to the mean, which is a fancy way of saying that the best investments over the past several years will often be among the worst over the next several years, and vice-versa. By rebalancing a portfolio, you’re aiming to sell hot investments before they turn cold, then use the proceeds to buy investments that are warming up. Doing this ensures that every asset remains represented at the level you find appropriate.

Let’s examine the behavior of stocks since 1972, a period during which the market had its share of hard times. The decline of the “Nifty Fifty” stocks during the market crash of 1973 and ’74 was at the time the biggest drop since the Depression, and during the “lost decade” we’ve just experienced, U.S. stocks posted their worst 10-year return ever, including the Depression.

Would rebalancing have helped during that time? Let’s find out. Join me in the plutonium-powered DeLorean and travel back to the year Al Pacino’s horse head beat out Jon Voight’s pretty mouth for the Best Picture Oscar.

The Asset Allocation Under Inspection
The investment portfolio we’re studying has the following assets:

  • U.S. large-cap stocks: 25%
  • U.S. small-cap stocks: 15%
  • International stocks: 15%
  • Real estate investment trusts: 10%
  • Intermediate-term government bonds: 35%

We’ll examine how this portfolio performed from 1972 (the first year with reliable numbers for each asset class) through the end of 2009, and compare the returns under two scenarios: one in which it is never rebalanced, and one in which it is rebalanced annually. We’ll then compare our back-tested portfolios to the S&P 500, since the typical American portfolio is dominated by S&P 500 stocks.

But first, let’s put our guinea-pig portfolio under the microscope to see what history has to say.

1972-2009 No Rebalancing Annual Rebalancing S&P 500
Annualized Return 10.4% 10.6% 9.9%
$100,000 Turned Into … $4,290,387 $4,624,511 $3,622,187
Number of Calendar-Year Declines 7 5 9
Worst Calendar-Year Declines (32.6%), (12.4%), (11.9%) (20.4%), (13.1%), (10.4%) (37.0%), (26.5%), (22.1%)
Source: My calculations using data from Ibbotson, MSCI EAFE, and NAREIT

Armed with these numbers, we can prove or disprove our three basic principles.

True or False: Rebalancing Always Significantly Improves Returns?
At first glance, the extra return gained from rebalancing our case-study portfolio doesn’t appear extraordinary: a mere 0.2% a year. However, the rebalanced portfolio is worth $334,124 more than its counterpart — an amount that is more than three times the original investment. And who wouldn’t want an extra $330,000 for about an hour of work a year?

It just goes to show how earning a tiny bit more, compounded over decades, can really pay off. We see this even more when comparing the annually rebalanced portfolio to the S&P 500, which earned 0.7% less a year but grew to “just” $3,622,187. The diversified, rebalanced portfolio was worth $1,002,324 more — that’s a 27.7% increase. Shazam!

That said, if you rebalance out of an asset that’s on an upward trend, you can actually earn less. Let’s break down the returns from our non-rebalanced and annually rebalanced portfolios by decade:

Annualized Returns by Decade 1970s* 1980s 1990s 2000s
No Rebalancing 8.6% 16.8% 12.3% 3.9%
Annual Rebalancing 9.0% 17.5% 11.8% 5.2%
*1972-1979

The benefit of rebalancing during the ’70s, ’80s, and 2000s was higher than the 0.2% annual increased return observed over the entire 38 years. But the 1990s were a different story; during that time, rebalancing actually reduced returns. That’s because U.S. stocks, particularly large caps, were on a tear through most of the decade. Rebalancing in those years would have required investors to sell those asset classes before they had run out of gas, then buy lower-performing assets like international stocks and Treasuries — which posted less than half the return of U.S. stocks during the 1990s.

However, U.S. stocks got their comeuppance (actually, come-down-ance) in the 2000s. One reason the benefit of rebalancing has been greater over the past decade (1.3% per year, on average) is that the rebalanced portfolio entered the 2000s with lower exposure to U.S. large caps, meaning it was more protected when they reverted with a vengeance.

True or false? False. The boost rebalancing gives to returns is inconsistent — sometimes big, sometimes small, sometimes nonexistent, depending on market conditions. However, in the long term, you can expect it to add a smidge to your returns, which could add a not-insignificant amount to the portfolio’s final dollar value.

True or False: Rebalancing Is About Managing Risk?
Look back at the table of our back-tested results, and you’ll see that the rebalanced portfolio was less risky. It had fewer “down” years — and the declines it did have weren’t as bad. A non-rebalanced portfolio is subject to “asset drift,” when winners grow to take up a bigger proportion of a portfolio. We can illustrate this by reviewing the allocations of our non-rebalanced portfolio at three points: (1) at the start of our study, (2) right before the dot-com bust that began in 2000, and (3) right before the “Great Recession” crash of 2008.

Time Large Caps Small Caps International Stocks REITs Treasuries
Beginning of 1972 25% 15% 15% 10% 35%
End of 1999 34% 28% 8% 18% 11%
End of 2007 22% 36% 16% 16% 11%

In each case, the portfolio became considerably more aggressive, eventually coming to hold less than a third of its targeted allocation to bonds — right before two major stock-market corrections. Mazahs! (That’s the opposite of “Shazam!”) By the end of 1999, the portfolio’s largest holding by far was U.S. large caps — on the eve of their worst decade ever. And by the end of 2007, more than a third of the portfolio was in U.S. small caps, the most volatile asset class in our study.

A study by fund company Vanguard shows an extreme example of what can happen to a non-rebalanced portfolio. The researchers found that a portfolio created in 1926 with 60% stocks and 40% bonds would have ended 2009 with 97% of its assets in stocks. This is the opposite of the approach most investors should take; in general, your portfolio should get more conservative as you approach and enter retirement. By determining a proper asset allocation and regularly rebalancing, the investor — not the market — determines the level of risk in the portfolio.

True or false? True … usually. Rebalancing can move you out of highfliers poised for a fall. The degree to which that reduces your risk depends on what you’re rebalancing your portfolio into. Which brings us to our next point …

True or False: The Stock-Bond Split Is Key?
If the investments in your portfolio tend to move together in the same direction and to similar degrees, rebalancing is less useful. Conversely, when those holdings don’t move in lockstep, rebalancing does a better job at managing risk.

In the investment world, that lockstep is known as correlation — the degree to which assets perform similarly in any given year. Broad categories of stocks — e.g., large caps and small caps, or U.S. stocks and European stocks — are at least somewhat correlated, often highly so. Stocks and bonds, on the other hand, are only mildly correlated, and most importantly, bonds tend to smell rosy when stocks stink. Thus, if the biggest reason to rebalance is to control risk (which is usually done by investing in bonds), then the most important allocation to monitor and rebalance is your stock-bond split.

Let’s return to our example portfolio but remove the bonds, instead adding 10% to large caps, small caps, and international stocks, and 5% to REITs. The results: The non-rebalanced portfolio posts an annualized return of 11.3% (turning $100,000 into $5,785,943), whereas the rebalanced portfolio returns an annualized 11.5% (ending with $6,328,103). Once again, we see a rebalancing bonus of 0.2% a year.

However, on the risk-reduction front, rebalancing added nada. Both portfolios experienced seven years of declines of similar degrees. The three worst calendar-year declines for the non-rebalanced portfolio were 38.1%, 23.2%, and 18.2%, and the three worst for the rebalanced portfolio were 38.6%, 23.0%, and 18.7%. The rebalanced portfolio earned higher returns in the 1970s, 1980s, and — interestingly — the 1990s. However, the bond-free rebalanced portfolio slightly trailed the bond-free non-rebalanced portfolio in the 2000s — the decade when risk reduction was needed most.

True or false? In general, true. Ensuring the right split between stocks and bonds can lower your risk of sharp declines — and of running out of money in the future.

Tips for Rebalancing
Enough theory! Here are some practical considerations when it comes to rearranging your portfolio.

  • Account for taxes and other costs. If rebalancing results in big commissions or tax bills, the potential boost to returns could easily disappear. Whenever possible, rebalance in tax-advantaged accounts — such as IRAs or 401(k)s — and keep costs low by limiting transactions to no-load funds and discount brokerages. That said, don’t let the tax tail wag the investment dog. Plenty of people held onto stocks in the 1990s just because they didn’t want to pay the capital gains taxes. The market took care of that for them — by significantly reducing or eliminating the gains.
  • Rebalance with contributions and withdrawals. You can gradually rebalance your portfolio with strategic inflows and outflows. If you’re still working, use savings to buy more of underweighted assets (those that take up less of your portfolio than current market conditions warrant); retirees, on the other hand, should sell what’s become overweighted. An analysis by asset manager and author Phil DeMuth found that selling what has performed the best over the past year could prolong the life of a portfolio.
  • Rebalance annually — at most. Rebalancing more than once a year (e.g., monthly or quarterly) is more trouble than it’s worth. You’ll spend more in time, costs, and taxes to get a lower return. In technical terms, such behavior is known as “silly.” In fact, you’ll likely realize slightly higher returns and lower transaction costs if you rebalance even less frequently than annually — perhaps every two to three years. For example, you could rebalance once an asset class reaches a certain level — such as being 20% below your target allocation, or 20% beyond it. Thus, if your goal is that a certain asset make up 10% of your portfolio, you’d rebalance once that asset declined to less than 8% or grew beyond 12%.

In the end, it’s most important that you choose the strategy you’ll really do. For ease of implementation, it’s hard to beat annual rebalancing. As asset manager Rick Ferri wrote in All About Asset Allocation:

What is best for you is [a plan] you will actually maintain without procrastination. Annual rebalancing is simple and cost-effective, and it takes only a little time each year to implement, which means that you are more likely to get it done.

J.D.’s note: I had intended to tackle re-balancing myself next week, but Robert beat me to it. That’s okay. He knows more about it anyhow. Instead, I’ll chronicle the process as I try to rebalance my own portfolio.

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