Prorate

To divide proportionately, so as to determine actual amounts owed by the buyer and the seller at closing. For example, if property taxes for a month are $300 and the seller owns the property for the first 10 days while the borrower owns the property for the remaining 20 days, the property taxes owed would be prorated so that the seller would pay $100 ($300×10/30) and the buyer would pay $200 ($300 x 20/30).