Understand the equation associated with calculating cumulative return. The equation reads:
Current price of security - original price of security / original price of security
The current price refers to the amount of money the security is currently worth. The original price refers to what you paid to acquire that investment.
Plug in the variables to the equation. Look at your investment portfolio and find the current price and original price for an investment you are currently holding. Say you bought $10,000 worth of stock and it is now worth $13,000. The equation would read:
$13,000 - $10,000 / $10,000 = cumulative return
Perform the calculation. Using the above example, the calculation would be:
$3,000 / $10,000 = .30
Convert the decimal to percentage form. The cumulative return would be 30 percent.