Calculate variance and input BLANK if a related Date column is blank

[Anonymous]

I need to calculate the variance between planned days to complete a request and the actual days taken to complete it. Below is a sample from my data : 

ID	Planned Start Date	Planned End Date	Actual Start Date	Actual Completion Date	Planned Days	Actual Days	Variance
101	15/07/2020	20/07/2020	16/07/2020	21/07/2020	6	6	0
102	17/07/2020	25/07/2020	17/07/2020	29/07/2020	9	13	4
103	20/07/2020	30/07/2020	23/07/2020		11
104	30/07/2020	10/08/2020	30/07/2020		12
105	02/08/2020	06/08/2020	02/08/2020	05/08/2020	5	4	-1

'Planned days' & 'Actual days' are calculated columns. I am using DATEDIFF to calculate the number of days between the two dates - start date & end date. 

Query: If the 'Actual End' date is blank then, how do I get the following results  :

Actual days to display a 'blank'.

Variance to display a 'blank'

I am using the following formula for the Variance column : 

Comp Var2 = IF(ISBLANK(TestWorkFlow[ActualCompletionDate]), " ", CALCULATE(SUM(TestWorkFlow[Actual Days]))- CALCULATE(SUM(TestWorkFlow[Planned Days])))

The error message I get is 

Expressions that yield variant data-type cannot be used to define calculated columns.

[amitchandak]

@Anonymous , first of check Planned Days and Actual Days should have data type number

Try measure like

sumx(Table,[Planned Days]-coalesce([Actual Days],0))

Sum([Planned Days])-coalesce(Sum([Actual Days]),0)

[Greg_Deckler · Accepted solution]

@Anonymous Try:

Comp Var2 = 
  IF(
    ISBLANK(TestWorkFlow[ActualCompletionDate]), 
    BLANK(), 
    SUM(TestWorkFlow[Actual Days])- SUM(TestWorkFlow[Planned Days])
  )

[Anonymous]

Thanks @Greg_Deckler 

I had to tweak the formula a bit and it worked. 

Comp Var2 =

IF(

ISBLANK(TestWorkFlow[ActualCompletionDate]),

BLANK(), CALCULATE(SUM(TestWorkFlow[Actual Days]))-CALCULATE(SUM(TestWorkFlow[Planned Days])))