prorate
verb [ T ]
uk/ˌprəʊˈreɪt/ us ACCOUNTING
to calculate a cost, payment, or price according to the number of hours worked, how much of something has been used, etc. in relation to a larger number of hours worked, a larger amount of something used, etc.:
The bonuses for part-time employees should have been prorated based on their hours.
proration
noun [ U ]
The Fund and Investment Manager may share facilities common to each, with appropriate proration of expenses between them.