I now wish to add two more number columns, one that adds a percentage(GST) and one that subtracts a percentage(Discount) to the existing sum of the formula. I then need to output the result to a new numbers column as formulas aren’t compatible with FORMS.

Hi @JustinB1994 - You can reference other formula columns within formula columns. So could you not just have two additional formula columns (using Total Cost as the name of your formula above):

With GST: {Total Cost} * 1.13 (or whatever your GST rate is)
With Discount: ({Total Cost} - ({Total Cost} * {Discount}))

If you ever need to use formulas but need actual numerical columns for automations, etc check out the General Caster App.