The Online version is only to prepare a current years tax return, which now is for 2019.
To file your 2018 with TurboTax, you would need the 2018 Desktop software (which is installed on your computer). Prior year returns must be mailed.
You can also go to the IRS & State websites for prior year forms to manually fill out & mail.
For tax years 2018, 2017, or 2016
You'll need to purchase and download the TurboTax software for PC or Mac as TurboTax Online and the mobile app are only available for the current tax year.
After installing the software, open it and follow the onscreen instructions.
Prior year returns must be paper-filed, as e-filing is no longer available. We'll walk you through that process when you get to the File section in the software.