To handle task-level estimates and time reporting, I have been using (roughly) the technique that Steve McConnell describes in Chapter 10 of Software Estimation. Specifically, when the time comes for me to create task-level estimates (right before coding begins on a project), I determine the tasks at a fairly granular level so that, whenever possible, I have no tasks with a single-point, 50%-confidence estimate greater than four hours. That way, the task estimation process helps with constructing the software while helping me not to forget tasks during estimation. I come up with a range of hours possible for each task also, and using the statistical calculations that McConnell describes along with my historical accuracy data, I can generate estimates at other confidence levels when desired. I feel like this method has been working fairly well for me. We are required to put tasks and their estimates into TFS for tracking, so I use the estimates at the percentage of confidence I am told to use.

I am unsure, however, what to do when I do forget a task, or I end up needing to do work that does not neatly fall within one of the tasks I estimated. Of course, trying to avoid this situation is best, but how do I account for forgotten/changed tasks? I want to have the best historical data I can to help me with future estimates, but right now, I basically am just calculating whether I made the 50%-confidence estimate and whether I made it inside the ranged estimate.

I'll be happy to clarify what I'm asking if needed -- let me know what is unclear.