Look at those huge answers for a simple question with a simple answer.
If using Turbotax online, you need 3 accounts with different user names and passwords (they can be linked to the same email) -- one joint and one for each separate spouse return. You don't pay for these accounts until you file, but if you decide to file separately, you have to pay for each return separately unless you qualify for free filing.
If using Turbotax installed on your own mac or PC (the desktop version, from a download) you can prepare 3 returns without paying extra, or you can prepare 1 joint return and then look for the "what if..." worksheet.
The key thing to remember is that when filing separately, both spouses must use the standard deduction or both spouses must itemize, even if there are not enough deductions to spread around. It is not allowed to load all the deductions on one spouse and the other spouse claim standard.
Most of the time, joint filing is better, but rarely it is not, the only way to know for sure is to test it.
