DateAdd Number of Intervals not showing for all rows

[Sunnie]

Hi, I'm trying to spread total hours of a task over a certain number of months.  I don't have an end date , but I do have a start date.  I thought simple way was to use DateADD , yet my outcome is not configuring for all rows. 

Duration Interval = DATEADD('STEP Resource Planning'[Start],[Duration(months)],MONTH)

I want to use this as my End Date column.  Wanting to know if this makes sense to do it this way, and if so, how do I have it calculate for all rows.

Thanks.  

[JW_van_Holst · Accepted solution]

Assuming you are using a calcuated column:

Duration Interval = DATE(YEAR('STEP Resource Planning'[Start]), MONTH('STEP Resource Planning'[Start]) + 'STEP Resource Planning'[Duration(month)]), DAY('STEP Resource Planning'[Start]))

[Sunnie]

@JW_van_Holst , oh my goodness, your Dax worked and look all the hours are in the months columns.. so thankful  do you know how many hours I've been trying to get this to work?   👼