I am trying to attach a stock basis calculation for a S-Corporation shareholder with respect to unallowed business loss from Sub S corp for 2019
That is not part of the tax return ... supply that information directly to the shareholder with the K-1.
You will not be able to e-file; you will have to print and mail your return.
you can use form 6198 at risk. if the S-corp losses and deductions exceed basis. then no supplement should be needed.
Thanks for the info!
Dennis