Created attachment 37012 [details] Reproduction file I have created a sample of when the issue occurs. IRR in apache documentation says that covers "20 tries" as shown here https://poi.apache.org/apidocs/dev/org/apache/poi/ss/formula/functions/Irr.html which is identical to Microsoft Excel https://support.office.com/en-us/article/irr-function-64925eaa-9988-495b-b290-3ad0c163c1bc This indicate that the result is the same between the two; however, in the case of apache poi, it seems that the result is returned as NaN (while excel returns the actual result).
I had to increase the iteration count and then POI calculates -0.009463562705856032 for the attached test case
r1894110 - it seems like the way that Excel calculates its iteration count is very different from how the POI code does because the attached use case requires a much higher iteration count than 20 (POI iteration count)
https://bz.apache.org/bugzilla/show_bug.cgi?id=64085 is also open and has a discussion about how Excel's IRR has some unusual implementation