This is why I've learned to always under promise and (try to) over deliver. Whenever I think a project may take me 4 hours, I tell them 3 days. 1 week = 1 month

This is why I've learned to always under promise and (try to) over deliver. Whenever I think a project may take me 4 hours, I tell them 3 days. 1 week = 1 month, and so forth. Another valuable technique is the Pomodoro one, dividing one's work into intense 25 minute chunks of time. One then starts to think about work in terms of number of Pomodoros, giving oneself better a better idea of quantities of work. There are other productivity and health benefits as well.