A moving average computes the average of a measure over a sliding window of periods, to smooth out short-term variations. In DAX, it is obtained with DATESINPERIOD or DATESBETWEEN in CALCULATE, or with WINDOW. You need to handle incomplete periods at the start of the series.
Example
CA 3 mois = AVERAGEX(DATESINPERIOD('Date'[Date], MAX('Date'[Date]), -3, MONTH), [CA])