To complete a prior year tax return using
TurboTax you would need to purchase and
download the prior year (2016) desktop
editions from this website, https://turbotax.intuit.com/personal-taxes/past-years-products/ as
TurboTax Online is for the tax year 2017 only. You will also need to print and mail your return as
e-file is only for the current tax year 2017.
For additional information on
completing your prior year(s) tax
return, please see the TurboTax FAQ below:
https://ttlc.intuit.com/replies/3301770