Sum all previous values

[ThomasWeppler]

Hi Power Bi comunity

I want to sum up all previous values for a specifik assignment.
Below you can see a table with three colums. An assignemnt ID which show which projekt we are looking at.
A month index which show how many month ago this row is relevant for. So month index 0 means that it is this month and month index -12 means that it was a year ago.
An omsætning which shows the earning for the specifik assingment in the selected month index.

But I also want a colum that add all the former vaues together.
You can see it below.

My question is what formular should I use to get the desired result?

[amitchandak · Accepted solution]

@ThomasWeppler , You have try a new column like

sumx(filter(Table, [month index]<=earlier([Month Index]) ),[omsætning])

or

sumx(filter(Table, [month index]<=earlier([Month Index]) && [assignmentid] = earlier([assignmentid]) ),[omsætning])

[ThomasWeppler]

Thanks for the quick respond.
Your second line worked perfectly.