I think we all start off like that. Managing expectations is the number one game here. A simple way to combat this is to just add a multiplier to whatever your

I think we all start off like that. Managing expectations is the number one game here. A simple way to combat this is to just add a multiplier to whatever your instinct is telling you. To add to what _sh was saying, the confidence value is a good idea. If you can explain to your client that you think it could take 3 weeks, but let's set expectations for 6 assuming some things go wrong, you're going to be a lot better off and have some breathing room. If you finish earlier, all of a sudden you're awesome. If your client doesn't want any details from you, just dumb it down to your multiplier estimate.