Start with a cautious scenario.
Use your own recent results when you have them. If you do not, try a range of attendance and purchase rates and see how much the result changes. The sample values in this tool are only there to demonstrate the calculation.
Separate revenue from what you keep.
A sale is not the same as profit. Refunds, payment processing, advertising, fulfillment, and production costs all affect the result. Include your time or additional production expenses in other fixed costs when you want the model to account for them.
Compare the plan with the actual session.
After the webinar, record registrations, attendees, orders, refunds, and costs using the same definitions. The calculator models purchases by attendees only. Replay purchases and later sales should be recorded separately or included in a clearly defined additional scenario.
Net contribution here is a planning estimate before taxes and any costs you have not entered. It is not a revenue forecast or a guarantee.