You can make additional payments in advance of your scheduled AutoPay payment. In many cases, the extra payment will be applied to your next month's bill.
This is because, with AutoPay, the payment process swings into gear on your billing date, which is the date the bill is issued, and falls 2-3 weeks before your due date. An extra payment you make may occur while your automatic payment process is already underway for the current month so that extra payment will be applied toward your next month's bill.
Here is an example. In this instance, the customer's bill was issued on May 1. He has decided to pay an additional $3 in advance of his regularly scheduled payment on May 14, but because his automatic payment process was already underway, the extra payment did not get applied to this month. By the following month, his accounts are in sync again and reflect the $3 advance payment. As a result, his automatic payment for June is $3 lower than normal.