One of the key skills you acquire on your way to a leadership position in software development is a bit of an innate gut feeling about exactly WHEN you are going to ship. However, there are times when your gut isn't enough and you need to be able to back it up with facts.
In the past, I created an Excel spreadsheet and a chart that mapped find rates, resolve rates, fix rates, tester and developer weeks to a logarithmic chart and usually came up with a gold date that was accurate within five days.
However, there are times when you have a lot of historical data on your side and you need to get even more granular. For times like that, Andrew Delin has posted a spreadsheet that could help.