Calculating the change in the market price of common stock lets you measures its performance. You can measure the market price change in either dollars or as a percentage. Using dollars allows you to quickly figure your profit or loss. For example, if the market price increased by $2 and you own 100 shares, you know you made $200. However, the percentage increase or decrease lets you measure the performance of the stock relative to the size of the investment. For example, that $2 increase is a lot better if the stock is trading at $10 per share than if the stock trades at $800 per share.

Research the stock price by going to a financial website and entering the name of the company or its stock ticker symbol. To figure the change, you'll need to find the current price and the prior price. For example, if you want to calculate the change in the stock price for the day, you'll need the opening price and the closing price.

Subtract the beginning price from the ending price to figure the market price change in dollars. If this number is negative, that means the stock has gone down in value. For example, if the stock opened at $31 and closed at $33, subtract $31 from $33 to find the change in dollars is $2.

Divide the change in dollars by the original price and multiply by 100 to figure the percentage change. In this example, divide $2 by $31 to get 0.0645 and multiply by 100 to get 6.45 percent.

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