Counter from 2 dates

Counter from 2 dates

Hi

I am trying to create a formula where it gives me a number by subtracting difference from 2 dates

Completion_Counter (result to go here)

Reported_Date - Date_of_Completion = Completion_Counter

Is this possible so for example if report by date is 20/11/2019 and Date of Completion is 21/11/2019 the result on Completion Counter will be 1

Thank you for help