Beginning freelance web developers often have issues deciding how much to charge for website development–they either charge too much, or far too often, charge too little. If they are not charging enough, they may even lose money from the experience.
A good estimate of the time involved in the project, plus management time and other tasks, multiplied by your desired hourly or daily rate, gives you a good starting point for a cost proposal.
The problem that often arises is one of unexpected development issues and time. It’s better to overestimate the time a project may take, and even miss a contract or two, rather than missing deadlines or overworking yourself. If, on the other hand, you complete a project before the deadline, you will have more time to tweak it, and your client will be getting a great deal more for their investment.