If, and ONLY if, you're in a position to quote around 10x or above your desired hourly salary on your absolutely nightmare worst case scenario, do you do a fixed price bid. ONLY then.
In all other cases, your position is that you're a specialist hired by the hour, at a (significant!) premium to allow for the fact that you can be dismissed without cause at moment's notice, and any estimates are best guesses, given the information available at the time.
Also, keep a private file of any and all diversions from the basis on which you gave any estimate. They are bound to exist (pretty much from day one) and except for the very most trivial projects, your estimate WILL be wrong.
Optimism comes easy to our trade. Learn to embrace pessimism, plan for the worst, expect the worst and then pray that your plans weren't too optimistic. "This time it's different"? When pigs fly.
you can be dismissed without cause at moment's notice
This is the case for most employees also. At least it's always been my experience. Only if you have a contract with a guaranteed term and specific early-termination conditions can you assume that you won't go in to work tomorrow and get fired.
In all other cases, your position is that you're a specialist hired by the hour, at a (significant!) premium to allow for the fact that you can be dismissed without cause at moment's notice, and any estimates are best guesses, given the information available at the time.
Also, keep a private file of any and all diversions from the basis on which you gave any estimate. They are bound to exist (pretty much from day one) and except for the very most trivial projects, your estimate WILL be wrong.
Optimism comes easy to our trade. Learn to embrace pessimism, plan for the worst, expect the worst and then pray that your plans weren't too optimistic. "This time it's different"? When pigs fly.
Good luck!