Regardless of account's billing period, traffic usage is calculated at the end of traffic cycle which is one month or less if traffic cycle is forced to close with a traffic limit change or other events, such as billing period closure, changing to another billing period, or other plan. For example, if you sign up on March 7 for a billing period of 6 months, traffic will be closed and reset on the 7th of each month.
The traffic run up during the last day of the traffic cycle is transferred to the next traffic cycle calculations.
