Sorry, I don't have time to write a detailed answer but here are couple of interesting things to know about software estimation (from a book I have at home but

Sorry, I don't have time to write a detailed answer but here are couple of interesting things to know about software estimation (from a book I have at home but forgot the name) : * For a known task, developer are usually too optmistic by about 30% * At the very beginning of a project, your estimation can be off by as much as 400%, by the time you have the UI done (at least in wireframe), your estimation can be off by around 25%. Also, I suggest reading the "Three points estimation" part of this article : http://www.projects.ed.ac.uk/methodologies/Full_Software_Project_Template/EstimationGuidelines.shtml http://www.projects.ed.ac.uk/methodologies/Full_Software_Pro... It's usually for "big" project, but the Three points estimation technique can be used even if you are by yourself. Also, it's more scientific than just "doubling" your number (check Standard Deviation on wikipedia if you want to understand how it work). Finally, with this technique, it's easy to spot tasks which have alot of uncertainty.