In a formula column, the SUM() function allows you to add the contents of several columns together.

Formula

SUM(Column1, Column2, Column3, Column4, Column5) 

Example 1

SUM(Amount before tax, VAT)

Configurator

Result

I have added the Amount before tax column with the VAT column.

Example 2

SUM(Amount before tax, VAT, 12.90)

Result

In addition to the example 1, I added 12.90 which correspond for example to the unimputable expenses of Colissimo.

NB: In the same logic, I can subtract a sum, simply by adding a negative number:

SUM(Amount before tax, VAT, -10)

Result