That makes it worth the effort to improve your ability to estimate projects. In You can start with something as simple as keeping a repository of project information, work breakdowns from your SDLC, estimates, and actual time spent by task. Such a simple approach can give you an informative history so that each new project builds on knowledge gained from the past. The rest was consumed by sick days, vacation, holidays, training, meetings, and administrative functions, such as filling out time sheets so we could track projects. Knowing this allowed far more realistic estimates.
Some software claims to help turn the act of managing development projects into a science.
This software, at the least, can help you turn informal record-keeping into a managed process. It can add further value if it helps guide you through the estimating process by culling from best practices and industry research, and if it provides rules of thumb for estimating. You should get the benefits of better estimating without adding a huge overhead. If you have to spend days gathering information, working abstruse formulas, or doing any other elaborate preparation, then stick with a pencil, an eraser, and the back of an envelope. It should permit you to export the results into a file format read by your project-management software so you can track actuals against estimates.