Hi @NanDeb ，
Please create following measure:
var cumulative_sales = CALCULATE(SUM('Table'[VALUE]),FILTER(ALL('Table'),'Table'[TaxDate] <= SELECTEDVALUE('Table'[TaxDate])))
var total_sales = CALCULATE(SUM('Table'[VALUE]),ALL('Table'))
IF(cumulative_sales <= total_sales * 0.8, cumulative_sales)
I think this is the result you want:
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.