formula: add difference when cell exceeds value to the next cell

Hi all,

 

I don't know how to solve the following issue. I want to automatically calculate colmn I.

I need to built the followin logic: when a cell exceeds a certain amount (column B), the difference has to be transferred to next month unless the limit of next month is also achieved then the amount has to be transferred to the next month and so forth.

I now created this column manually. 

 

Column B represents the maximum quantity which we can sell per month. 

The sum of Column C, D & E represents the actual revenue. However we need to take into account our limit in column B. For January for example we have sold for €25 but we can only deliver €20 so the

real Revenue will be €20. The open amount of €5 needs to be transferred to next month. However for

February we have already realized €135 but can only deliver €50. We need to transfer the €5 (jan)+ €85 (feb) to next month. In March we realized  €85 and we can do €100. We can transfer €15 out of the 90 to achieve €100 euro. The open amount of €75needs to be transferred to April....

I hope someone can help me out

 

Thanks a lot!