I'm developing an application which will list members who have not paid their any previous month's fee and a separate list for those who have paid the fee. So, lets say a member who will be paying fee through out the year, each month and if he didn't pay fee for march 2013 then app should highlight him as un-paid member. What would be best practice to achieve it. Adding fee invoices for whole year already in database when member is added then loop through his payments to check if fee is paid or not, or add a validation date for member on his each payment, for example payment made in Feb 2013 then member is valid till 28.02.2013. Check if date today is 28.02.2013 then he has not paid..