After you install the download it is exactly the same as the CD. You can do it offline. BUT when do you usually install and when do you print to mail it? Unless you install later close to April 15 there are weekly updates you need otherwise your return might not be right. You should at least do an update right before you finish and print. And when you start do you copy last year's .tax data file back to your computer so it will transfer into the next year?
