auto sum a different column and end at the first blank cell

[dawondr]

Hi,
I have a very basic sheet that I use to track my forecast each month. It is an evolving doc meaning I just add the next month to the sheet so I also have a log of what I had in the past.
If you can look at the attached example, you will see there is no set number of entries for a given month. I'm wondering if I can automatically have the new month I add also create an autosum for that month. I am very flexible where that information can be shown. Yellow or blue cell would be best but I'd even be happy even if it was in the green cell and summed down instead of up. (this will make sense when u see the sheet).
If it is more than a couple of keystrokes just tell me that it is more work then the benifit of automating and I'd be fine with that answer too, autosumming is easy enough that I can manually do it each month but I think I'm just missing something here in automating the step.

Thx in advance for your time,

Dave