Copying Formulae

The workbook I have attached shows a template ( yellow) that my app copies 12 times onto a worksheet (January shown on this illustration).
The problem that I have is how to deal with the formulas that I would like to add to the YEAR TO DATE half of the template which would sum up the previous YTD with the current value.
I have to deal with the fact that December (the first month) is different from all the others as it has nothing to sum to. Secondly that a formula in the template would need to refer to negative column numbers and I don't think Excel allows those.
Is there a way to use the template which I would prefer or do I have to do something in the completed year sheet?
John

Here is an updated worksheet with some numbers and formulas. I hope this will make more sense.
John

Glenn, any thanks for your help. It does work on my app.
A propos of your last post, what should I call a stand alone group of procedures which my colleagues can use, without any particular knowledge of Excel to present data from SQL server in a form which meets there needs? Application or app seemed about right to me.
John