How Much Will It Move? Calculating Risk with Fast Beta

If only there were a way to guess how much a stock might move when the market does...Oh, there is. And it just got better.

When calculating risk, you can use all kinds of tools to compare a stock’s current volatility to its past volatility. However, one of our favorite charting indicators in thinkorswim^®—beta—allows you to compare a stock’s volatility to the volatility of a market index, such as the S&P 500 (SPX), the Dow 30 (DJX), the Nasdaq 100 (NDX), or the Russell 2000 (RUT).

Consider a little refresh. Compared to the S&P 500, say a stock has a beta of 1.25, and the S&P 500 moves up 1%. That means that, theoretically, the stock would move up 1.25%. But we thought this indicator could be a little better—more useful. How? By creating “fast beta” (see figure 1).

Old Vs. New

The downside of using regular beta when trading shorter-term volatility is that it uses a long set of price data that is unweighted, thereby considering older price movements as equally valid to more recent price movements. This discounts the possibility that current volatility might be significantly different relative to the long term. Fast beta places more emphasis on recent price movements and requires less historical data.

The interpretation of fast beta is roughly the same as that of regular beta. But keep in mind that the time over which we measure is shorter, which might work better when calculating, say, a hedge on a short-term trade.

The “modified” portion that gets us to fast beta is the use of a weighted moving average instead of a simple moving average. Using a weighted moving average gives fast beta a calculation that is more sensitive to recent price movements in a security, as well as in its benchmark.

Just like beta, fast beta measures the systematic risk of a security, and the sensitivity of that security’s returns to market returns. As well, a benchmark “market” is selected and defined to have a fast beta equal to 1.0. Just like beta, stocks with fast beta greater than 1.0 are more volatile than the market, whereas those with lower fast beta are less volatile. In short, if a security has a fast beta of 2, and the market is down 10%, the security is expected to be down 20%. Stocks with fast beta equal to 1.0 are said to move with the market.

How To Find It:

1. Log into thinkorswim.
2. Go to the Charts tab.
3. Enter a symbol and press to pull up a chart.
4. In the upper right, above the chart, click Studies > Add Studies > Alpha Studies > FastBeta. 

The default index used to compare is SPX. However, you can choose one of the other four main indexes (Nasdaq 100 [NDX], Russell 2000 [RUT], Dow Jones Industrials [DJX], and the Nasdaq Composite) through the “Edit Studies” under the studies menu as well.