How to substract months dynamically in a repeating group


My problem is quite simple. I want to build a table where each line represent a month (for a report page).

First line will be this month, next line will be last month, third line will be 2 months ago, etc.

My question is :
How to I substract the current cell index from current date?

Just add a minus sign before “Current cells index”

I tried but I can’t add a minus sign before

You are right. I forget this. You can use a not visible input field where you set intial value to Current cell index * -1
Use this input value in the +month
Example here: