Monthly Forecast Automatic Spreads

My goal is to re-spread over or under monthly variances as months progress and actuals are updated. I'm doing this manually for over 120 project budgets. I wish to automate the re-spreading of the variances (whether under or over). The original budget allocation should stay static as the re-spreads are updated. Any ideas or resolution is greatly appreciated. I've attached a sample of what I have...

Edit:
I forgot to add that some projects may start anytime during the initial year and some even can cross over to the following year. Therefore the budgets will be multi year. I've updated the attachment -