Software estimation is an art best practiced with a bit of math and a few examples. This app gets you started with a first cut at best and worse case estimates based on your own experience.
Quickly calibrate the app with your own sample projects. Then model how many days of effort a new software project will take to complete. The app accounts for the diseconomies of scale that come with large projects. You can also characterize your project organization and how it impacts the estimate.
Nothing replaces detailed analysis and estimation, but this gets you started with best and worst case scenarios.