Quarter accrual on a 12 months basis

Hello

i am going to do my best to explain how i may require your help building a formula.
on the attached document, you will see a very simple accrual formula that add and withdraw amount from a month output (colomn c).
this document attached works when its a jan2012 thru dec 2012 12 month basis.
but what if i use the same number and now use a may 2012 thru april 2013? how can i have a formula that will give me the exact same total?
can u please help me ?? i am desperate, i m actually beyond desperation

I cannot see any accruing, month 1 and 2 seem simple calculations, month just sums 1 and 2 and negates.

you are correct, thats how i did my calculations thinking it was what we called accrual/provision,
i actually wanted to deploy those simple calculations but that will combine to one at the end of every 3 months. like if i have only a sum in the end of march it will generate the combine formulas of january, feb & march.

Is this what you mean

L123: =IF("T"&INT((MONTH($B123)+2)/3)=L$122,$C123*$C$116/12,"")
L124: =IF("T"&INT((MONTH($B124)+2)/3)=L$122,$C124*$C$116/12,"")
L125: =IF("T"&INT((MONTH($B124)+2)/3)=L$122,-L123-L124,"")

and copy across to column O