Hey there @paulschmidgall! Great question. TSheets is billed based on users marked as "Active" in TSheets, regardless of if they have tracked time or not. Of course, you can always archive any employees for whom you do not wish to be billed/track time.
You can see an up-to-date billing estimate at any time by going to Company Settings and selecting the Account & Billing tab. Your estimate along with a current count of active users will be at the bottom, next to "Monthly estimate."
Let me know if you have any questions on this. :)