A price-weighted average is a simple mathematical average of several stock prices, and is often used to construct a price-weighted index. Perhaps the most well-known stock index in the U.S., the Dow Jones Industrial Average is a price-weighted index.

In practice, using a price-weighted average to calculate a stock index means that the higher-priced stocks have a disproportionate influence on the index's performance. Here's how to calculate a price-weighted average, and how it works.

**Calculating a price-weighted average **To calculate a price-weighted average, or any arithmetic average for that matter, simply add the numbers (stock prices) together, and then divide by the number of stocks in the average.

For example, if you want to calculate a price-weighted average of four stocks, with prices $100, $70, $60, $30, you can do so as follows:

**How it works **To illustrate how a price-weighted average or index works, consider three popular stocks:

**Apple**,

**Microsoft**, and

**Intel**. As of this writing, the share prices of these stocks are:

Company |
Share Price |
---|---|

Apple |
$94.69 |

Microsoft |
$51.18 |

Intel |
$28.80 |

Using these share prices, we can calculate a price-weighted average of these three stocks as:

Now, let's say that Apple releases some incredibly positive news tomorrow, and its shares jump by 20%, or to $113.62. This would raise the price-weighted average to $64.53, a 10.8% jump.

On the other hand, if Intel stock experienced the same 20% move to $34.56, it would translate to a price-weighted average of $60.14, or a move of just 3.3%. So Apple's 20% move has more than three times the impact of Intel's on our three-stock index.

Of course, this is a simplified example. It's not likely that just one of these stocks would move, and the other two would stay exactly the same, but you get the idea. Plus, there aren't any notable indices made up of just three stocks.

In a more complicated example, the more expensive stocks in the 30-component Dow Jones Industrial Average such as **3M **($156.17) and **Goldman Sachs** ($144.91) would have a much greater influence over the index than lower-priced components such as **Cisco Systems** ($26.12) and **General Electric** ($29.22).

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*The Motley Fool owns shares of and recommends Apple. The Motley Fool owns shares of General Electric Company. The Motley Fool recommends Cisco Systems and Intel. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.*

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