XIRR formula not working when adding extra cash flows

Originally Posted by MrShorty

I often find that simply opening a spreadsheet like this in LibreOffice calc or in Google sheets allows their seemingly more stable algorithm to calculate correctly without further changes.

And in this case, my own "XIRR" implementation in VBA calculates an IRR that causes the NPV to be exactly zero without a "guess".

I use a Newton-Raphson algorithm, but I calculate the exact derivative.