Federal returns: Although you can paper-file as many federal returns as you want using the Desktop software, only five (5) of those can be e-filed per IRS regulations.
State returns: If you have more than one state attached to your federal return, up to three (3) of them can be e-filed. Keep in mind that many nonresident state returns can't be e-filed anyway, so if you're doing more than one state, focus on e-filing the resident and part-year resident return(s).
Tax professionals: Our license agreement doesn't allow TurboTax to be used for commercial or professional tax preparation. If you need to e-file multiple returns because you prepare taxes for a living, take a look at our ProSeries or Lacerte software.