Regardless of whether the job is a contract job or a cost plus job the logic is the same.
$ Gross profit = total invoiced to date – actual amount spent to date
% Gross profit = $ Gross profit / total invoiced to date
The amounts given are without tax.
They also represent a margin style calculation as opposed to a markup style calculation. The rest of the Buildxact system works on markup so the gross profit % in a job will be different from your markup % in an estimate even if all job costs are exactly as expected.
See more on markup here: