When you allocate your assets, you decide—usually on a percentage basis—what portion of your total portfolio to invest in different asset classes, like stocks, bonds, and cash or cash equivalents. You can make these investments either directly by purchasing individual securities or indirectly by choosing funds that invest in those securities.
As you build a more extensive portfolio, you may also include other asset classes, such as real estate, which can help to spread out, and thus moderate, your investment risk.
Asset allocation is a useful tool to manage systematic risk because different categories of investments respond to changing economic and political conditions in different ways. By including different asset classes in your portfolio, you increase the probability that some of your investments will provide satisfactory returns even if others are flat or losing value. This is known as diversification. Put another way, you're reducing the risk of major losses that can result from over-emphasizing a single asset class, however resilient you might expect that class to be. This is especially true if your assets are "uncorrelated," meaning they react to economic events in ways independent of other assets in your portfolio. Stocks and bonds, for instance, often move in different directions from each other, which is why holding both of these asset classes can help manage risk.
While you can recognize historical patterns that seem to indicate a strong period for a particular asset class or classes, the length and intensity of these cyclical patterns are not predictable. That's why it's important to have money in multiple asset classes at all times. You can always adjust your portfolio allocation if economic signs seem to favor one asset class over another.
Financial services companies make adjustments to the asset mix they recommend for portfolios on a regular basis, based on their assessment of the current market environment. For example, a firm might suggest that you increase your cash allocation by a certain percentage and reduce your equity holdings by a similar percentage in a period of rising interest rates and increasing international tension. Companies frequently display their recommended portfolio mix as a pie chart, showing the percentage allocated to each asset class.
Modifying your asset allocation modestly from time to time is not the same thing as market timing, which typically involves making frequent shifts in your portfolio holdings in anticipation of which way the markets will turn. Because no one knows what will happen, this technique rarely produces positive long-term results.