When you add more people to a team on the Premium Plan we'll make a one-time, prorated charge to your credit card to cover your new team member's account for the remainder of the current billing period.
As an example, suppose your team is on the Premium Plan, which costs $8 per user per month when billed monthly. You add a new team member 10 days into your billing period and there are 20 remaining days in the month. The per-day cost for each user is $8 / 30, so we will make a one-time charge of $5.33 ($8 / 30 days * 20 days) to your team's credit card on file.