My investment has an initial cash outflow of $1000 followed by series of losses on this investment thus all remaining cash flows are negative.

I was interested in knowing my loss in terms of internal rate of return for this investment so I tried using Excel IRR function with my data listed below but I was given a #NUM! error in Excel 2010 using the IRR function.

My cash flows are as follows

-1000
-644.89
-338.33
-87.34

I did try an alternative IRR function that is part of tadXL Excel add-in which is no longer available online and it reported a correct IRR for this investment.

So what makes tadXL report an IRR for all negative cash flows and Excel IRR function is unable to find the internal rate of investment where investment makes no money and there are all losses.