By what date is the account payment due?

To view the date of payment for your account, go to the Account settings - Payment plan. 
In this section, on the right side, you will see the "Payment plan" block. In the "Next payment" field, you will see the date of payment. If for some reason you can't pay for your account right now, you can take a 7-day deferral. 
View the entire payment history in the "Payment archive".
A notification will appear in your account 7 days before the payment is due.

You will receive an email 5 days before the payment date. 

Note: only the account owner and the account administrator with the rights "Access to account setup and payment" can see and receive the notification by email.