Months / Years in Contract

BjoernSchaefer 

you can try to use below DAX to create two columns for year and month. However, I can't get your explaination of value column.

month = 
VAR _start=minx(FILTER('Table (2)','Table (2)'[contract]=EARLIER('Table (2)'[contract])),'Table (2)'[Date_invoice])
VAR _month=DATEDIFF(_start,'Table (2)'[Date_invoice],MONTH)+1
return if(_month>12,if(mod(_month,12)=0,12,mod(_month,12)),_month)

year = 
VAR _start=minx(FILTER('Table (2)','Table (2)'[contract]=EARLIER('Table (2)'[contract])),'Table (2)'[Date_invoice])
VAR _month=DATEDIFF(_start,'Table (2)'[Date_invoice],MONTH)+1
return if(mod(_month,12)=0,int(DIVIDE(_month,12)),int(DIVIDE(_month,12))+1)

Btw, it will be better if you can share your sample data.