A prorated payment is a partial payment; you only pay for the remaining days of the first month.
How to calculate prorated payment:
Monthly Parking Card Cost / Number of Days in the Month = Price per Day
Price per Day * Remaining Number of Days in the Month = Prorated Payment
$30 per month / 30 days in the month = $1 / day
$1 * 15 remaining days in the month = $15 prorated payment