How does billing work? Is it the # of active users at the end of the cycle?

[Chris McGroarty]

Hi, we had added in 120+ users on Monday of this week 12/19.  This more than doubled the amount of existing active users, which were around 90.  However, there was then a change of direction and we decided to deactive those new 120+users, and that was all done yesterday, 12/22.  Our billing cycle doesn't close until 12/27.  And out of those 120+ users, only about 10 had accepted their invite and logged in, but even then those people didn't really do anything.  

So my question is this...will we get billed for ~90 users, since the ones that were added were removed back out before the billing cycle ends?  Or will also get billed for the 120 users, since they were invited?

[Trudy Claspill]

The Billing section under https://admin.atlassian.com includes billing estimate pages for your next billing date. Have you reviewed those?

[Steffen Opel _Utoolity_]

That's a good question and surprisingly hard to answer:

And out of those 120+ users, only about 10 had accepted their invite and logged in, but even then those people didn't really do anything.

By chance I've come across a definite statement for that part of the question within section Add users to a cloud site:

Additional users are automatically counted towards billing even if they don't accept your invite or log in. [emphasis mine]

As for adding and then removing users within one billing cycle, I'm not aware of user identities being tracked for the purpose of billing, so this seems to be a less sophisticated approach than with some other SaaS products like Slack.

In turn adding and then removing the same user should yield the same pricing as adding a new user and removing an old user, i.e. ultimately it comes down to the effective user count at the beginning of the next billing cycle, see Centralized user management:

Remove a user if you don’t want them to appear in your organization or have access to your products anymore. You won’t be billed for a user once they’re removed. You must invite the user to your organization again if you want to reinstate their access [...]

Suspend access to remove a user’s access to your organization temporarily. You won’t be billed for a user when their access is suspended. Restore access to give the user access to your organization and products again. [...] [emphasis mine]

As already hinted on in Trudy's answer, the ‘Billing’ section for your site within https://admin.atlassian.com/ indeed surfaces the effective user count and resulting pricing for each product and app in the ‘Users’ and ‘Next price estimate’ columns.