On Wed, 6 Aug 2008 19:27:01 -0700, Jerry W. Lewis
wrote:

It appears to relate to the fact that your return is less than your
investment. I am not an accountant, but I would think that descibing a loss
as a negative return would be more useful than simply reporting that you
didn't make any money. Excel 2007 converted ATP functions to worksheet
functions; it would be interesting to know if it also changed this behavior.

Jerry

Jerry,

I'm not sure why.

The OP's function, on the sheet he posted, actually returned a very small
number (not 0). 0.000000298023224%


Including a "guess" that was negative, albeit quite small, resulted in the
probably correct result.

=XIRR(B3:B44, A3:A44,-0.000001%) -- -9.83%


So far as reporting zero when there is a loss, not necessarily the case. This
series, with no guess supplied, returns the expected amount:

1/1/2008 -500
2/1/2008 -500
12/31/2008 900


XIRR(values,dates) -- -10.42%


--ron