Calculate points for year based on last 180 days

[Diogie]

I have a spreadsheet for my employees to calculate attendance points for the year. My 2007 excel doesn't have enough columns to put everything on one tab so I have each month on a separate tab and a 13th tab that calculates the points per month. What I need next is a way to calculate the points based on the last 180 days because points drop off after 6 months. Attached is my spreadsheet if anyone has any ideas that may help me.

It'll also have to calculate whent he year changes too.

Thanks in advance!!