For estimating something (doesn't matter if it's software or what) this is a useful process: Has something similar been done before? How long did the previous

For estimating something (doesn't matter if it's software or what) this is a useful process: Has something similar been done before? How long did the previous examples take? Why do you think this time will be different? The last question is not to catch you out. Maybe typical splash pages take people a few days but you're really fast at design, or they needed more polish. If I take a week normally to write a blog post and know that this one is longer than usual, maybe I need to add some time. Perhaps you're adding some copy but this time it doesn't need to go through legal. Whatever the difference is, try and start with previous known data and then adjust from there. You shouldn't predict it'll only take you a day to get this blog post out if it takes you a week every time and you've got to prepare for a talk at the same time. More detail and an example from Kahneman: http://www.mckinsey.com/business-functions/strategy-and-corporate-finance/our-insights/daniel-kahneman-beware-the-inside-view http://www.mckinsey.com/business-functions/strategy-and-corp...