While inside the Invoice, there is a totals bar at the bottom of the window that will give you the Estimated Profit.
The Estimated Profit is determined in one of two ways:
If you entered receipts in Production, the Estimated Profit is the total amount invoiced (subtotal) minus the total amount of receipts entered in the Production Module.
If you did not enter receipts or actuals, the Estimated Profit is the total of the Fees category in the Invoice Module -- plus -- any line item markups -- plus -- any job markup/category markup -- minus -- the Production Expenses.
Note: If your job has an Agent Rate in the Financial tab, the Agent's cut will be subtracted from the Estimated Profit.