I am going to disagree with your approach. Your ex husband was alive for 12 months in 2011. He had income during that time period. What he received in 2011 is divided by 12 to get the monthly gross. I realize this makes for a lower gross than if you divide by 11.5 months, but the child support guidelines are based on actual income received, not earned.
My question to you is: if a paycheck is dated 12/17/11, wouldn't the next paycheck 2 weeks later be 12/31/11?
I hope you found this response to be of assistance. This response shall not be considered the rendering of legal advise but instead a general response to a general question. While Avvo is a wonderful resource, nothing can be a substitute for an in-depth consultation with an attorney in the jurisdiction in which the law is to be applied. This response shall not be deemed to create an attorney-client relationship, nor shall it create an obligation on the part of the attorney to respond to further inquiry from the questioner.