Excel uses iteration to arrive at a result, starting with the guess (if provided) or with .1 (10%) if not. If an accurate IRR can’t be calculated after a fixed number of iterations, the #NUM error is returned. A better guess will prevent this error.


The values array must contain at least one positive value and one negative value. Values should be in chronological order. If IRR returns the #NUM! or an unexpected result, adjust guess.

Dave Bruns

Hi - I’m Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.