Finding the total percentage gain or loss on a portfolio requires a few simple calculations. First, you should understand how percentage gains or losses are found on an individual security. To find the net gain or loss, subtract the purchase price from the current price and divide the difference by the purchase prices of the asset. For example, if you buy a stock today for $50 and tomorrow it is worth $52, your percentage gain is 4% ( ($52  $50)/$50 ).
Finding the daily return on your portfolio requires a different approach. Because the stocks will usually have different purchase prices, a percentage gain in one security may not be equivalent to an equal percentage gain in another. Simply adding the individual percentage returns will not give an accurate measure of portfolio return. By adjusting the above method of finding a stock's return, you can find the percentage return of a portfolio. Instead of using the purchase price and current value of the stock, you will do your calculations based on the total value of your portfolio. For example, on June 1, your portfolio is valued at $14,500. After a week of market activity, your portfolio value increases to $15,225. Your percentage return on your portfolio for the week is 5% ( ($15,225  $14,500)/$14,500 ).
For more information on evaluating your portfolio, read Equity Portfolio Management Mechanics.

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The monetary return experienced by a holder of a portfolio. Portfolio ... 
Estimated LongTerm Return
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