Time Estimation

I need help.

I keep underestimating the time required to do a programming task at work.  can anyone give me tips on how to better my time estimation?

>>11
>Think how long it feels, double it and use the next unit up.  So if it's something that ought to be a half-day task, say one week -- and you'll probably be right.

so if something will take 1 month, i say 2 years?