Sum By Date Paid

I am trying to sum rows based on unusual criteria: i.e. A table of date c2:t9 contains details of expenditure for 16 periods for insurance and motor expenses. i want to convert this to a cashflow format and reflect when the item is actually paid, so if it is paid in february, march, etc (given in the original table) I want to add the totals in the months preceding the set date. also, if the criteria is a number <12 then i want to add up the preceding amounts if the period number is a factor of that number e.g - criteria is 3, then i want to add rows 1-3 and put in period 3, 4-6 and put in period 6.