Taking remaining value and sharing across remaining months?

Hi,

I've got a spreadsheet which works like this. There is a total value which is spread across 8 months. Taking into account some other things which affect it.

What I want to do is if for example januarys target was 45 and the actual was 5, there would be 40 missing so I want to share this across the remaining months and add it onto there target. So say febuarys target was 55 it would add the extra from january onto its target making it 60.

How would I go about doing this?

Heres an image to explain (A bit more detailed i hope)

Example.png

I need to do this across each month.
EDIT - these cells already have a formula in which give its current value (its a sum value1/value2)

Hello and Welcome to the forum can you please upload a book

Like this !!!