Give three estimates. One if everything goes well, the most optimistically you can imagine. One representing the most likely path. And one representing the worst-case scenario. Let your manager digest from there.
If you have a bad manager (e.g. they would just use the best-case scenario estimate and ignore the others), average the estimates, 1 part best case, 1 part worst case and 4 parts normal case. Then try to make sure you are giving a set of estimates, not just one, and usually it will average out.
Step two of having a bad manager is finding a different situation, whether via internal transfer or a new job.
For me I had one manager where every time he said "how long will is take?", I got that feeling of fear and dread in my stomach. I suppose the problem was that he wasn't asking for an estimate, he was asking for a specific date when the project was fully deployed. He wanted pinpoint accuracy, even though that was impossible. Missing or undershooting a target would have him bringing you into a room where he would start interrogating you about what he perceived as a personal and professional failing on your part.
So anyways myself and others started pushing back and refusing to give estimates and instead just saying "it will be ready when its ready" and when pushed giving super vague time frames like "a few months". He did not like that.
If you have a bad manager (e.g. they would just use the best-case scenario estimate and ignore the others), average the estimates, 1 part best case, 1 part worst case and 4 parts normal case. Then try to make sure you are giving a set of estimates, not just one, and usually it will average out.
Step two of having a bad manager is finding a different situation, whether via internal transfer or a new job.