When does the discount column appear in the invoice, and when does it disappear?

There’s no direct option called “hide discount column”, but whether the column appears is decided in two ways: on the invoice creation screen by the How to Apply Discounts setting, and on the printed invoice by whether any item has a discount.

First: the discount column on the invoice creation screen

From Invoices Settings → Pricing & Discounts → How to Apply Discounts:

Option	Discount column in the items	Invoice total discount (Discount & Adjustment tab)
Invoice Total Discount Only	Hidden	Shown
Discount per Item	Shown	Hidden
Both Invoice Total and per Item (default)	Shown	Shown

To hide the discount column from the items: choose Invoice Total Discount Only and save. This applies to invoices, estimates, sales orders, notes and returns.

Second: the discount column on the printed invoice or PDF

• The discount column appears only if at least one item has a discount, and it disappears automatically if no item has a discount.
• The How to Apply Discounts setting doesn’t affect printing; old invoices with item discounts still show the column.
• The invoice total discount doesn’t appear as a column, but as a Discount line in the totals, and only if it’s greater than zero.

To hide the column from the print: don’t put discounts on the items, and use the invoice total discount instead (it then appears only as a line in the totals).

Can I hide the column from the invoice layout?

Invoice Layouts has no option to hide the discount column; you can only rename it (Discount). For a custom design that always hides the column, you can edit the template’s HTML, or contact the custom development team.

Summary: when does the discount column appear and when does it disappear?

Where	Appears when	Disappears when
Invoice creation screen	How to Apply Discounts = per item, or both total and per item.	How to Apply Discounts = invoice total discount only.
Printed invoice / PDF	At least one item has a discount.	No item has a discount.
Discount line in the totals	The invoice has a discount.	There’s no discount at all.