To prorate (adjective pro rata) is to divide a value in proportion to some other value.
Security expenses are shared pro rata, based on my percentage space occupied.
I occupy 500 sqm of 2,000 sqm premises (That 500 sqm is 25% of the 2,000 sqm total)
Security expenses are R12,000 per month.
My pro rata share of security expenses is 25% of R12,000 or R3,000.
My monthly license is charged pro rata, based on numbers days usage per month.
My license starts on the 10th of a 30 day month (The 10 days is 33.3% of the 30 day total)
License charges are R12,000 per month.
My pro rata license expense is 33% of R12,000 or R4,000.