Help with dax to calculate conditional statement by month

I have a problem getting the right formula in my report.  I only have two tables, the activity table then just a standard date table to slice time frames.

ActivityTable:                                        DateTable

Day                                                       Month&Year etc.

Amount

Flag

The records are a list of days, an amount for that day, and a Y or N to indicate if it exceeded a threshhold.  Looks like this

example:

The end result I am trying to build is to get to by month, what percentage of days exceed the threshold

so like this:   And would need it to do this for each month as dates are added.  Basically count how many days within a month/year had activity, then calculate the percentage of those days that had "Y's" flag.  So in this example, January had for activity dates and the threshhold was 500, and only 1 of the 4 exceeded that (Y)

I thought I could count # rows by filtering the table for Y but when I do that, it is not by month.  It it just the whole table count of Ys.  

Does anyone know how to do this?  Thanks very much.  New to dax and it is very confusing switching from tableau 🙂