Cut a line in a Line chart

The following dax measure should help you 

Actual Values Until Current Month =
VAR LastActualMonth =
CALCULATE (
MAX ( 'YourDateTable'[Date] ),
'YourActualsTable'[Actual Value Column] -- Replace with your actual value column
)
RETURN
IF (
MAX ( 'YourDateTable'[Date] ) <= LastActualMonth,
[Your Original Actual Values Measure], -- Replace with your original Actuals measure
BLANK ()
)

If you need more help, do not hesistate to share your model or field name 🙂

You can detect the date of max date with actual and return blanks if either before or after.

Var dt = max( dates[year month] )

Var tbl= 

Addcolumns(

Allselected( dates[year month] ),

"@actual", [actual column]

)

Var lastDate=

MAXX(

Filter( tbl, [@actual] > 0 ),

Dates[year month]

)

Return

If( lastDate <= dt, [accumulated actual] )

you could calculate the accumulated plan using measure 

if data not found for that month, you can give blank