Total Annual Return Calculation

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Can someone help me understand how the annual total return is calculated on the BP Rental Property Calculator? It seems like something was changed in the calculator in the past couple of months because I used to be able to come up with the same number as the calculator when doing it by hand, but now the numbers don't match up. Here how I am calculating it: (Total Profit if Sold/Total Invested Capital)/Time (in years) When I do this by hand, it matches for the first year, but after that it doesn't. 

Thanks in advance for the help!