Prorata Billing allows you to pay your balance on a fixed day of the month for products/services no matter what day they were ordered. When you order, you will be charged the prorated amount which is calculated by dividing the total price by the number of days in the month and then multiplying by the number of days left until the first (1) of the month.
There is a cut off date at which time you will be paid for the next month on top of the first months. That day is the 20th of the month. We do this so that we can avoid extremely low charges and you don't have to make 2 payments within a matter of a few days.