Calculating percentage of column in date range

I am trying to work out a way of calculating the percentage of staff who have completed training within the last year within a column to flag up our overall training compliance. 

I have already used conditional formatting stay green if in date, yellow when 90 days off date for training due and red if the date has past. I use the expiry date in the future as the entered number so if they complete today (24/4/25) I would enter 25/4/26. 

I am only using one column for dates so would want values from B2 to B86 to be counted and the percentage of dates that have not gone past today to be worked out as a percentage and put at the bottom of the column in B88. I also want to have a system that can have staff added and deleted as they join/leave without messing up the formula calculation if that is in any way possible. 

Many thanks