Sickness Absence by Month

Hello,

I'm currently calculating sickness absence for my company, I've created a data entry form and want it linked to a overview by month. E.g. John Smith has been absent between 01/04/15 - 30/09/15 which equates to 131 working days, I'd like this broken down by days lost per month. I've attached the example excel sheet.

Thanks in advance.

Joe