Iowa revenue stamps, from the statute rather than a rule of thumb
How Iowa Code 428A.1 computes the real estate transfer tax a seller pays at recording.
Iowa Code section 428A.1 puts a tax on a deed when the consideration is above five hundred dollars. The tax is eighty cents for each five hundred dollars, or fractional part of five hundred dollars, above that first five hundred. Eighty cents per five hundred dollars is $1.60 per $1,000. County recorder pages in Iowa describe the same rule as $1.60 per thousand with the first $500 exempt.
The net-proceeds ledger on this site applies that rule. On a price of $500 the tax is zero. On $100,500 it is $160. The line is small next to commission, and it is the one most national calculators leave off because it is Iowa's.
Commission, concessions, repairs, and carrying costs on the ledger are inputs. The defaults are estimates for the metro, not a listing agreement and not a closing statement. The stamp line is the statutory amount. A closing agent prepares the statement that actually gets paid.