Portfolio Toolbox
Balanced rocks

Portfolio Rebalancing

When you select a target asset allocation you will generally have both stocks and bonds in your portfolio. Over time, the percentage of stocks and bonds in your portfolio will drift from your target which changes the risk profile of your portfolio. You can rebalance your portfolio back to your target asset allocation to maintain your desired risk tolerance.

Rebalancing is a risk management strategy.

For example, if your target asset allocation is 60% stocks and 40% bonds and over time your portfolio drifts to 62% stocks / 38% bonds, rebalancing will sell 2% of stocks to buy bonds to return your asset allocation back to 60/40. Over long periods of time, stocks tend to outperform bonds and if you start with a buy & hold strategy of 60/40 and never rebalance, your portfolio style could drift to 70/30 and become more volatile than your risk tolerance allows. Rebalancing back to 60/40 will return your portfolio to your target asset allocation and risk tolerance.

When to rebalance

Every trade made has the ability to enhance or reduce portfolio returns, rebalancing is no exception. While a side effect of rebalancing can be to enhance portfolio returns, the timing of rebalancing is key. A common assumption held by investors is that rebalancing forces investors to sell high and buy low, however that isn't always the case. In the case where stocks and bonds are both lower, rebalancing causes you to sell low and buy lower.

There are two popular strategies used to determine when to rebalance portfolios:

Time based Rebalancing is performed at fixed intervals such as annually, quarterly, monthly, etc. Investment advisors often recommend that clients rebalance portfolios on their birthday so that all investors are not rebalancing on the same day.
Deviation based Rebalancing is performed when asset allocation deviates from your target by more than X%. This allows winners to "run" to a certain threshold before selling them.

How to rebalance

The mathematics to rebalance a portfolio are fairly straightforward. Simply take your portfolio balance and multiply it by your target stock asset allocation (%) and that gives you your target dollar amount for the stock portion of your portfolio. Likewise, use your target bond asset allocation (%) to determine your target dollar amount for the bond portion of your portfolio.

Here is an example of a two security portfolio. Enter your target asset allocation %, symbols and portfolio total and your target dollar amount for each security will be displayed.

% Symbol Target dollar amount
Stocks
Bonds
Portfolio Total $

Below is a backtest of this portfolio with an initial starting balance of $10K. The blue line represents the performance of a buy & hold portfolio, while the red line represents the performance of this portfolio rebalanced when it deviates more than 5% from the target asset allocation.

To view how the actual asset allocation of these two portfolios changes over time, click on the animate checkbox below to see the monthly results. You can also move the slider to select a particular month to display. Note that the longer the timeframe, the more the actual asset allocation can drift from your target asset allocation, changing your portfolio's risk profile.



Here are several methods you can use to rebalance your portfolio:

Automatic rebalancing

Rebalancing takes time to monitor your asset allocation and execute rebalancing trades. Most investors do not have the inclination to rebalance on their own. If you are reading this, you are not the typical hands off investor. Fortunately there are mutual funds available that automatically rebalance themselves and allow investors to take a set it & forget it approach to their portfolio. These are balanced funds and target date retirement funds.

Balanced funds maintain a fixed asset allocation over their lifetime no matter the market conditions. Target date retirement funds on the other hand gradually become more conservative (or less volatile) as they approach the target date of the specific mutual fund. In the United States, target date retirement funds are typically the default option in employer's 401k plans. If you are just getting started with investing, a target date retirement fund corresponding to your retirement year is a good choice to start off with. Vanguard offers a variety of balanced and target date retirement funds.

What is the optimal rebalancing strategy?

Which rebalancing strategy is best? It depends. Each approach has the capability to increase or reduce returns, however finding the optimal rebalancing strategy for a portfolio is only knowable in hindsight and is uniquely dependent on the timeframe which is measured.

Rebalancing is not a one size fits all approach for improving your portfolio returns, it is a risk management strategy. That is why there isn't a firm answer on the best strategy for when to rebalance.

Taxes

Here are a few notes about rebalancing and taxes. When you sell a security to effect a rebalancing trade, that sale will have tax consequences in a taxable account. Typically it is better to rebalance in your tax deferred or tax exempt accounts. There can be situations where it may be advantageous for you to rebalance in your taxable account to take advantage of tax loss harvesting or tax gain harvesting depending on your specific tax situation. If you do intend to sell a security in a taxable account it is advantageous to only sell securities that you have held for at least a year and a day to take advantage of lower long term capital gains taxes. You should consult with your tax advisor about the tax impact of selling securities in your taxable account.

Resources

Monitoring your risk level and rebalancing