calculated according to, or as a share of, the fixed rate for a larger total amount

a pro rata payment/pay increase 按比例计算的报酬／加薪

It's €20,000 pro rata, but I'm doing half the full number of hours, so I'll be getting €10,000. 按比例算是2万欧元，但是我只做了全部时间的一半，所以我该拿到1万欧元。