prorate
verb [ T ] uk/prəʊˈreɪt/ us/proʊˈreɪt/
finance & economics specialized按比例计算（成本，付款或价格）
to calculate a cost, payment, or price according to the amount of something that has been used, in relation to the fixed rate for a larger total amount
The rental will be prorated if occupancy does not begin on the first day of the month. 如果房客不是月初入住的话，租金将按比例计算。
See also: pro rata