using DATEDIFF function not using DATE fields

[Anonymous]

I'm trying to use the DATEDIFF function, however its not giving me the option to select my fields which are formatted as DATE. 

DATEDIFF(DATE1, DATE2, Interval) 

For DATE1 I have a table and field  = Campaigns[StartDate] - this does not show up when I try to use this for DATE1. The only options that populate are other measures. None of the DATE fields I have in the table show up. 

I hope this makes sense. Again - the fields are of the type DATE.  For DATE2 - I would like to use TODAY(). Ultimately, I'm trying to calculate the number of days between TODAY and the StartDate field. 

Thanks for your help! 

[camargos88]

@Anonymous ,

Keep in mind that when you work with measures you need to check if the function expects scalar values or not. Mostly of calculations functions you need to work with scalar values.

[camargos88 · Accepted solution]

@Anonymous ,

Are you using measures ? If yes, try using this column inside a SELECTEDVALUE function.

[Anonymous]

That worked - thank you. 

This is what I used - 

days between = DATEDIFF(SELECTEDVALUE(Campaigns[startDate]), TODAY(),DAY)