The cost of an annual license to Yellowdig software is defined by the number of Active Users expected to use Yellowdig in the contracted term (annually).
Active User: any student, instructor, or administrator at your institution who logs in to Yellowdig within the contracted term. The definition of an active user is not defined by the number of times a user logs in over the course of the contracted term, or how many different courses they participate in. Their actions and participation are unlimited.
To project the number of active users on Yellowdig, you would use the number of faculty and enrolled students in each of the courses and/or departments and/or organizations that you intend to give access to use Yellowdig. You should underestimate this number, as you will pre-pay for that number of active users. No "unused active users credit" will be provided should you use less than the projected number of active users you've paid for.
Should you go beyond the number of active users you paid for upfront, you have a 10% overage buffer before you'd need to pay for additional active user licenses. So you may use 110% of your active users before you're required to pay for additional licenses to Yellowdig. You are able to purchase more licenses at any point during your annual contracted term.