Distribution of a time span across months

Question

I a process have a Start date of 1/1/2022 and end date of 3/15/2022, date is in it's own field.

Now I have a field for every Month in the Year: J F M A M etc.

I want to calculate that my process covers 100% of January and February and 50% of March. In order to calculate this, I added the start and end date for each month below the field like this :

Screenshot

Any help how I can calculate this would be appreciated.