Comment: Re:X, Y, Z, Buffer Overflow Error (Score 1) 521
Really the trick is just getting a detailed feature-set and being good at estimating how much time things will take you. After you do that then you simply double the amount of time (because things don't always go smoothly).
My mum told me this rule for estimating back when I were a lad. Make your best guess then double it. Still works to this day.