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system
calculating a simply complicated return?
user
since you have the balance at equal periods and the cash flows at the period ends, the best return calculation in this case is the true time-weighted return. see http://en.wikipedia.org/wiki/time-weighted_return#formulae  so, notwithstanding some ambiguity about your figures, here is a calculation using the first three periods from your second table. giving a total return over the three periods of -23.88% if the periods are months, multiply by four to annualise.
assistant