Charge Types can be set up to create invoice lines that are percentages of the invoice total for handling the likes of surcharges or discounts. The following example shows a charge type that will provide a 20% discount on the invoice total.
Under User Charge Rate From, the Invoice Total option has been selected. Note that when adding a new charge type this option is not shown until you press the Advanced button. Invoice lines that are generated from this charge type will have the invoice total set as their rate, and then the quantity can be set to the percentage to be discounted. In this case the Default Quantity is set to -0.2 which will when multiplied by the invoice total will give the correct 20% discount amount. Showing this rate on the invoice is unnecessary and would add confusion so Show Rate and Quantity has been unticked to exclude them for these lines.
The Sort Order has been set to Second to ensure that when the invoice is printed the discount line appears after the other invoice lines (where the sort code on their charge types are set to First).
Add this Charge Type to the Default Charge Types for the client. When adding to the client defaults leave the Default Quantity and Default Rate as zero so that the charge type will dictate the quantity and rate.
The invoice that is generated will print like this: