Hi,
thank you so much for your response and as always its a relief 
We have devided budget in months through Fund not Fund center. 2ndly we are not controlling budgets of revenue we are usibg it as assessment to see what was planned and what is actual. Key factor of deriving FM assignments is posting date in derivation rules. Comming to your solution can u please guide me a little how to build such a rule in fm derive?