[golergka]

Badly.

It is not a joke comment. I could go into a lot of detail about methods that I've used, but it's the most important and valuable piece of knowledge that I've gotten out of this experience: we're bad at this. No matter how we do it, that's the thing that we should never forget.

[mrfredward]

I second this. I have made tons of mistakes estimating, but the fact is that for all the foolish mistakes I've made--forgetting things, not asking the right questions, and jumping the gun on making a prediction--I've probably never had enough information to make a good estimate.

Almost every project runs into an unforeseen roadblock. The less experience you have with a sort of project, the more true this becomes. You can't account for things you don't see coming, so the usual answer is to arbitrarily pad estimates, and of course arbitrary padding is usually wrong.

A project plan is more useful for finding bottlenecks than predicting an end date. So unfortunately, the best tip I can offer is to make sure people are aware of the uncertainty involved, and beware of people who expect it to be straightforward.