Software Estimation Without Guessing

Multi-Level Decomposition

When the small number of large parts leaves me with parts still too big to estimate, I often take the first (in development order) of those parts and break it down again.

Can you estimate the first item? If not, you can decompose that first item in a similar fashion. Now you’ve got smaller, more easily estimated items. If it’s still too big, you can repeat this strategy.

In extreme cases you might need to go to a third level of detail, but realize that each time you’re increasing your uncertainty. That’s to be expected. The longer the time horizon, the more uncertain you are. You don’t want to forget about that uncertainty, though, lest you fool yourself.

I don’t think I’ve ever gone beyond three levels of doing this—but ...