The value of a stock will move up and down during the market day as investors buy and sell shares. Traders who move in and out of stocks with short-term trades want to know the daily return on an individual stock. Other investors just like to know how much they made if one of their stocks has a big day. The calculation method can also be used with a stock market index to determine how much the market moved during the day. Calculating returns involves dividing the difference between two values by the starting value. Stock declines result in negative returns.
Find the closing share price of a stock for the current day and the previous day on a financial website, such as Yahoo! Finance, Google Finance or MSN Money. The prices can be found by entering the stock symbol in the "Get Quotes," or similarly named, box near the top of the financial website's homepage.
Subtract the previous day's closing price from the current day's close. If the stock increased in value, the number will be positive. A down day will result in a negative number. For example, assume your stock finished yesterday at $24.75 and today the price fell and finished at $22. Subtract $24.75 from $22 to get negative $2.75.
Divide the result by the previous day's close and multiply by 100 to convert to a percentage. Continuing the example, divide negative $2.75 by $24.75 for a result of negative 0.1111. Multiply by 100 to get a daily stock return of -11.11 percent.