Yeah, definitely over-estimate. And do so based on your confidence (and ill-confidence) of the overall effort. Generally speaking, the larger the project may be

Yeah, definitely over-estimate. And do so based on your confidence (and ill-confidence) of the overall effort. Generally speaking, the larger the project may be, the more likely a small error in estimation results in a huge problem later on. If you find yourself quoting projects that you've "been there and done that" before then those should be easy to make a solid profit on and still quote an "accurate" amount for. After all, you know (far better than your client) how long it will take you and how much effort it will require, as well as what the pitfalls are likely to be along the way. With totally uncharted territory, simply charge more and put a longer timeline on it. I've even been in situations where the cost was deliberately over-priced and had a huge timeline on it far beyond what was needed (mainly because we didn't really care to do the project much but we quoted a massive amount anyways) and we got it. That's another trick; if you don't want the work in the first place, don't just say No, let your quote be a reflection (with a massive premium on it) that says you'd do the project if some insane price was paid for it. On the flip side, you want to add in huge premiums when the work is not well understood or well-known by you. Even though someone else out there in the world might have a better grasp of the problem domain and could estimate better, you're the one doing the work, after all, and should price it according to the risk of the unknown.