There are estimates and estimates. As a rough ballpark figure (1 day, 1 week, 1 month, 3 months, 6 months, 1 year, 2 years, 3 years, 5 years) estimates are doa

There are estimates and estimates. As a rough ballpark figure (1 day, 1 week, 1 month, 3 months, 6 months, 1 year, 2 years, 3 years, 5 years) estimates are doable and reasonable. It's also reasonbable and doable to let scope be the factor rather than time. "Tell us the most important thing and we'll do that and deliver the results every couple of weeks, tell us when what you have is good enough". You can also do fairly accurate estimates when you're basically just doing the same thing as you've already done many times or when the customer doesn't have to give much input. Most of the construction industry is like this because it's older, goverend by physics and building codes and we have a few standard models for most things. Most of the software industry isn't like that. However for something new, where the customer doesn't really know what he wants in much detail accurate estimates aren't really possible. In this case anyone who purports to give you an accurate estimate is either lying or using extensive padding. Customers, and non techinical people in general, have a hard time understanding what things are difficult / important from a complexity perspecitve. Often seemingly "simple" (to them) changes are actually very complex, and sometimes the other way.