I estimate by guessing how long it will take me to code then multiply it by 3 and round up to the whole unit.

10-30min work = 1 day
2 day work = 1wk
1wk work = 2-3wks
1month = 3 months

If only I didn't have to deal with other people that take forever....

That and I feel lately whenever my boss ask me for a "quick" change or feature... I literally have to go "down boy down, stop thinking your in a candy store" like he's a little kid.