Bandwidth for dedicated servers is calculated live on a rolling 30 day cycle. This type of calculation does not reset bandwidth every month to 0 GB, but instead re-calculates daily for the past 30 days. Please see below for examples:
Example:
Current Date: November 5th
Bandwidth Calculated for: October 5th to November 5th
Example 2:
Current Date: July 27th
Bandwidth Calculated for: June 27 to July 27
Important: Bandwidth between multiple servers is not pooled. Each server has it's own bandwidth allocation that cannot be shared between servers.