Want to subtract two dates for absence leaves

Summary

Hi all, I am trying to create a column with the total days in an absence.

Content

I am trying to subtract the start and end dates of the leave to create that information however, it is not working for some reason. The start date of the leave and the end date are both in separate columns, and I want to subtract the values in them. I am wondering if I have to create the dates as all numerical to aid the calculations? I am trying this formula: min(start date) MINUS max(end date) however it is coming up as an error.