With Monthly, Quarterly, Semi-Annual and Annual billing you will receive an invoice 30 days before the 1st of the month of when your payment is required to continue your service. Your invoice will be due on the 1st. If you are paying with credit card on an automatic payment, the invoice will be charged to your card 5 days before the due date, in case an problem come up.
When you first sign up for the service, if before the 15th of the month, your invoice will be for the prorated amount for that current month. Which will be due the same day. If you sign up after the 15th, you will receive an invoice for the prorated amount for the current month and the amount for the next month. Which will be due the same day.