pro-rata

/P R OW1 R AE1 T AH0/
adverb
  1. 1

    (of an allocation) In proportion to some factor that can be exactly calculated.

    โ€œTenants who have given 30 days' notice who do not leave on the last day of the month will be charged on a pro rata basis.โ€

Source: https://en.wiktionary.org/wiki/pro%20rata, https://en.wiktionary.org/wiki/pro-rata