Comparing figures over 6 months (SUMPRODUCT)

Hi All,

I need to compare figures for the past 6 months, for the same period that we are in in the current month i.e if 20 days have elapsed this month I want to add all the figures for the first 20 days of April, March etc. I tried using SUMPRODUCT but cant seem to get it to work, should I be using something else?

I have attached a sheet with the way my data is set out, only working days are shown on the sheet so a month will not neccessaraly start from the 1st, any help will be greatly appreciated