It is possible to use formulas in the format editor if you need to process variables with all the usual arithmetic operators.

The condition is to have the necessary fields in the format to be able to use them. If they are not variables already used elsewhere in the format, they are usually put at the bottom of the page, or at least grouped together in the same area for convenience:

When you put them in this area for later use, don't forget to uncheck "Visible" so that they won't be printed there:

Formulas are created by clicking on the A+B button on the toolbar:

then in the area where you want to put it.

Practical example: the theoretical vacation balance until the end of the year :

Start by giving a name to the formula (no spaces or special characters in the title):

To calculate the theoretical entitlement until the end of the year, it is necessary to take the current vacation balance and add the theoretical entitlement of future months.

The formula will therefore be:

Three fields are required: the current month's vacation balance, the employee's vacation entitlement per month and the current period(month)

After that, you just have to use the usual mathematical operators.