You will be billed either monthy or yearly, depending on your plan.
Customers with a yearly billing cycle get 20% off on the cost and they get charged on the same day every year.
Customers with a monthly billing cycle get charged on the same day every month on the payment date.
At the end of your payment cycle, the number of people in your account are added and multiplied by the package cost to compute your bill. This is automatically charged to the card on file.