This is finger-in-the-air approach, which seems doomed to fail. For a start, it relies on your buddy having exactly the same career experience as you, and any

This is finger-in-the-air approach, which seems doomed to fail. For a start, it relies on your buddy having exactly the same career experience as you, and any new project being an almost exact match to previous projects you have worked on. It doesn't take into account the unknowns, and doesn't break the task down into components that you could at least attempt to quantify. Personally I go through a short mental breakdown of the project, trying to partition it in my mind into smaller jobs. Based on my years of experience I will then have a gut feeling for certain aspects of the project. If any job is more than 3 days long, then I try to break it down further. If I can't mentally break it down, then I need to spend some time researching why that is (investigate the unknowns). Once everything has been broken down, and I have reduced the unknowns as much as possible I add contingency. Anything that I feel has the potential to be problematic I will add more contingency to, or add additional research time.