Bookings are always billed to the credit card associated with the account.
A hold will initially be placed on the credit card for the cost of the trip. After a short period, the charge will be directly applied to your credit card.
If there is any driving credit available on the account, it will automatically be applied at the time of booking.
Additional mileage costs, toll charges and traffic violations will be added to the trip charges as soon as they are received and processed by Zipcar. It is not unusual for these charges to appear several weeks following the trip.