Air is a service that's billed on a monthly basis per user, which means that subscriptions are paid upfront for the month ahead. You will see prorated seats on your invoice if you add or subtract Member seats or Guest invitations.
Prorated fees are a partial fee for the time between starting the new service and your bill date. And while it might seem like your bill is higher than expected, these prorated fees do not reflect your regular monthly subscription and will not appear on future bills unless you change or add a user.
When you sign up for Air, your initial charge is for the users on your account when you check out for the first month, paying in advance. As you add more users, your future bills will contain:
Any prorated fees for added or subtracted users
The monthly fees for the next pay period
If you change or add a user in the middle of your bill cycle, you'll only be charged for the time that user is on your account. So on your paid invoice, you'll see three types of charges:
Standard Monthly Charge
Here's how prorating works. If your bill date is on the 8th and you add a $30/month Member seat on the 20th. You'll have a prorated fee for the 18 days between the date you added the user and your next bill date - that would be indicated by Remaining Time on your invoice. The Remaining Time charge would be $18 since you're paying for 18 days of the service instead of a full month. If you removed a user on the 20th instead, it would be indicated by Unused Time, crediting your invoice $18.
Prorated charges can often be surprising, particularly if the changes to your account were made iImmediately following the bill date. But the good news is the reverse of this is also true. If you remove users from your account, you'll receive a credit for users you've been charged for but haven't kept.