Variables based on Date

Hello,

I'm trying to calculate Inventory Days on Hand (DOH) using DAX. I've created Variables for each month that contains the number of production days in the month. Example: VAR Jan = 19, Feb = 20, etc. I'm just not sure how to write the DAX formula to calculate DOH. In Excel the formula would be Production Days / Inventory Turns. How do I get it to dynamically change for example when I want to review February data. I apologize if my question does not make sense. I'm a newbie to this community. Any assistance is greatly appreciated.