Monthly subscription
When you initially subscribe, you will be charged for the number of users in the account marked as Active.
After that, an invoice is issued once per month. The charge reflects the number of users marked as Active at the time of renewal. There are no prorated charges for adding or removing users mid-period.
Annual subscription
When you initially subscribe, you will be charged for the number of users in the account marked as Active.
After that, the subscription renewal invoice will be issued once per year. The annual renewal charge reflects the number of users marked as Active at the time of renewal.
Prorated charges on the annual plan
When you add new users mid-period, you will be charged for their subscription to cover the prorated charges from the date added till the date of the next renewal (the end of your yearly billing cycle). The invoice for the prorated charges is issued and sent to you when the total of prorated charges surpasses a threshold of $150.00. And then, for the next invoice, the charges are gathered again till the threshold of $150.00.
When you remove users from the account, you will get a credit for the remaining portion of their annual subscription charge. The credit will be applied to your next invoice.
Every time the number of users in the account changes (increases or decreases), a pair of items appears on your invoice:
Remaining time is a proportional debit. It represents the charge/cost to finish the current subscription cycle (from the date of the user count change until the next renewal date) with the new user count.
Unused time is a proportional credit you receive for the unused portion of the subscription with the old user count, from the date of the user count change until the end of the billing cycle.
To calculate the actual cost of the added users, you need to deduct the unused time charges from the remaining time charges.