I'm surprised to be the first to write: You estimate because you do contract work for US state/local government, and the paperwork and process is horrible, and

I'm surprised to be the first to write: You estimate because you do contract work for US state/local government, and the paperwork and process is horrible, and so you have to write a contract where you lay out the whole final product up front, and you have to decide what to charge for the whole thing before even starting. That number is going in the contract. It isn't going up. Fun fact: ISTR at least one locality where, if they found out you started work before the contract was signed, there was some law (or maybe it was a policy, but in any case, no one could break it) forbidding the department from paying for said work. Once I asked about doing time and materials instead of big design up front. The government department I was working with started saying how that would require them to certify hours, and there was a whole process, and I got the feeling that if I pressed the issue then they'd rather just find someone who could give them a dollar amount up front.