Bandwidth Resetting Monthly But Accounts Not on 1st of Month

[WestBend]

I searched the forums and couldn't find a clear cut answer to this question.
As i understand it (hopefully ) the bandwidth exceeding email and the bandwidth monitor are monitoring an accounts usage on a calendar month basis and not based on when the user's account was setup. So if a user signs up in the middle of the month with 10gbs of usage / month they are going to accrue 15 days of usage and then have it reset back to 0. Then they will accrue another 15 days and perhaps now exceed that 10gbs of total since they started but the server will only think they have used say 5gbs since the 1st of the month. I am sure this is a standard problem and the solution is staring me in the face but can anyone tell me what they do in their own world in regards to this problem? I am thinking that the only way to do this is to pro-rate the monthly charge to the 1st of the upcoming month and make their billing date from that point forward the 1st of every month.

Any advice/experience in this would be greatly appreciated.

[PWSowner]

We bill for the hosting monthly as of the day of creation, but measure bandwidth by the calendar month and bill for excess bandwidth with the next hosting bill for monthly plans, or give a seperate bill for bandwidth if the hosting was paid quarterly or yearly.