The acronym ROI stands for return on investment, which is a way to measure the performance of various investments, including a stock portfolio. To calculate the ROI for your entire portfolio, you need to include the cash you have in the account, even though it may not be actively invested. To calculate the ROI for the stock portfolio as a whole, you need to know the starting and ending value of the entire stock portfolio.

Add the value of all of your stocks and the cash in the account on the starting date for which you want to calculate the ROI. For example, if want to calculate your ROI from January 1, 2010, through January 1, 2011, and on January 1, 2010, you had $5,000 of stock A, $8,000 of stock B and $2,000 in cash, the starting value of your portfolio equals $15,000.

Add the value of all of your stocks and the cash in the account on the ending date for which you want to calculate the ROI. For example, if want to calculate your ROI from January 1, 2010, through January 1, 2011, and on January 1, 2011, you have $5,400 of stock A, $8,100 of stock B and $2,010 in cash, the ending value of your portfolio equals $15,510.

Subtract the starting value from the ending value to find the net return on your portfolio. In this example, subtract $15,000 from $15,510 to get a return of $510.

Divide the return by the starting value to calculate the ROI of your stock portfolio including cash expressed as a decimal. In this example, divide $510 by $15,000 to get 0.034.

Multiply the ROI of your stock portfolio including cash expressed as a decimal by 100 to convert to the ROI expressed as a percentage. Completing this example, multiply 0.034 by 100 to find that the ROI of your stock portfolio, including cash, equals 3.4 percent.

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