The annual plans are billed per company per month. As each company is added, throughout the billing cycle (year) the cost is billed immediately for the prorated annual license cost. That cost is determined by the package selected.
The monthly plans are billed at the beginning of the cycle. Each company that is added in the middle of a billing cycle is tracked and billed at the beginning of the next cycle for the prorated amount of month that was remaining when that respective company was added. For this reason, there are occasions where the bill appears to be higher than the agreed-upon price. This is caused because the new cycle begins with a bill for all of the companies added and the prorated amounts for the companies added during the prior period.