Damit I always get in trouble after I give a deadline to any task :/
My estimation of work done is poor

Those feels

To paraphrase @moshmage, always estimate high. And, as a "bonus", never allow others to negotiate your time down. If you finish early, clearly communicate that things went smoothly with no issues.

I've had people argue with me, but they tend to shut up when I break down the development, estimated hours debugging, code review, release schedule, and testing. It's very easy to throw buffers into each piece of the pipeline for one large buffer overall.

And on a final note, don't let others negotiate time away from pieces of the process for finishing a stage early. Some horrible managers will try to do that. It takes away from your overall buffer for when things go horribly wrong.

Check out the book Software Estimation: Demystifying the Black Art

@Christine I could marry you right now. I have no idea who you are, but after the day I've had this book is a godsend.