To prorate is to work out a charge from the real share of time or use, not from a full, round price. If a monthly fee is 3,000 dollars and you join on the 16th, the company may prorate it: you pay only for the days you actually have. Landlords prorate rent when someone moves in or out mid-month. Offices prorate bills; insurance can be prorated when a policy is cut short. The word belongs to business and billing, and it is especially American. British writers often keep the older phrase and say a cost is calculated pro rata. It sounds fairly formal. Though actually, people stretch it a little: any total split by a fair share — money, time, even holiday days — may be called prorated. The tidy idea does not change: not the standard full sum, but a sum that matches what you really received.

按比例分攤、按比例計算。美式動詞；台灣合約、帳單通常直接寫中文，較少出現這個英文詞。英式較常保留 pro rata。