Prorating is based on the percentage of the current bill period that the product has been in service.
Product proration type is In Advance.
Product service start date is 02/23/99.
Monthly charge is $12.12.
Bill period start date is 03/1/99.
Bill period end date is 04/1/99 (this is the start date of the next bill period).
The percentage is calculated using the following numbers:
Duration Used
The duration of the product, in seconds, from the product service start date to the bill period end date.
From 02/23/99 up to, but not including, 04/1/99. The Duration Used = 3,196,800 seconds.
Duration Per Cycle
The duration per cycle is the duration, in seconds, from the bill period start date to the bill period end date.
From 03/1/99 up to, but not including, 04/1/99. The Duration Per Cycle = 2,678,400 seconds.
Percentage
The percentage is the Duration Used divided by the Duration Per Cycle, plus 1 (add 1 to the results of the division, because the product is prorated in-advance).
(3,196,800 seconds ¸ 2,678,400 seconds) + 1 = 2.19 %.