Ask HN: Can you show me your budget calculation from your first ask?

Paige Craig in his recent article on how he did not invest in Airbnb (https://arenavc.com/2015/07/airbnb-my-1-billion-lesson/) discloses Airbnb's budget calculation before their first round of investment and describes how he corrected some unrealistic assumptions. What are the guidelines for creating realistic budget calculation? Are you willing to share yours? I don't mind if it is anonymized but it would be great if it was annotated/explained. Thanks.