From now on I am going to estimate all of my software projects like this:

• Figure out how many objects (Java classes, db tables, XML files, something else depending on language) will have to be created or modified.
• Give myself a full eight-hour day for each of the above, no matter how small each change might be.

The results might seem ridiculously large. Eight hours to change one line in a XML file? But trust me, problems will always come out of nowhere to eat up that slack time. The other advantage to this approach is that it forces you to actually list out all the places where you plan to touch the code before you do it.