Hi @nolan0716 ,
You can try code as below to create a measure.
VAR _SELECTDATE =
MIN ( 'TableName'[Updated Month] )
VAR _RangeStart =
EOMONTH ( _SELECTDATE, -4 ) + 1
SUM ( 'TableName'[Opportunity] ),
ALL ( 'TableName' ),
'TableName'[Updated Month] >= _RangeStart
&& 'TableName'[Updated Month] < _SELECTDATE
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.