On the date you purchase your policy, we charge you the monthly premium for the first full month of coverage. Your next charge will come out 15 days after the start date of your policy; this charge is for the second full month of coverage. Then that date is the date you will be charged every month following.
We have to charge you 15 days in advance just in case a payment declines or if your policy is going to cancel for any reason, so you can either correct the issue or get set up with insurance elsewhere.
Below is a diagram of how the monthly billing cycle works: