Alberto Ferrari shows how you can calculate running totals in DAX:
A very common calculation in DAX is the year-to-date calculation (YTD), which aggregates values from the beginning of the year all the way to a certain date. A simple implementation uses the predefined DATESYTD function:
Sales YTD :=CALCULATE([Sales Amount],DATESYTD('Date'[Date] ))
But click through to see when this function stops being useful and what you should replace it with when it does.