To insert a subtotal on a purchase

The Purchases window should be displayed. (To find the Purchases window)

Choose where you want the subtotal to be inserted:

If the line on which you want to insert the subtotal is empty -- no transaction is entered on the line, and it's not a blank, header or subtotal line -- click in the line. (The subtotal will be inserted here.)

Click on a line where there is a transaction, blank, header, or subtotal line entered on the line. (The subtotal will appear above the line.)

Select Insert Subtotal from the Edit menu.