The tax proration is an allocation of the property taxes between the Seller and Purchaser that is determined by their contract. It is not required, but it is customary. In Washtenaw/Livingston Counties the most commonly used proration is the “due date in advance” method. This treats the property tax bill like a newspaper or magazine subscription — when you pay your tax bill on December 1 it is treated as buying government services for the period starting on December 1 and ending on November 30 of the following year. So in a transaction closing on February 1, the Purchaser will reimburse the Seller 10/12ths of the previous December’s tax bill. This is because the Purchaser will occupy the property for 10 months of the 12-month period that started the previous December 1.