You may not have used the same account. Many people have multiple accounts without realizing it. Or did you use Free Edition last year? Or perhaps you used the desktop software in the past.
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Did
you use Online TurboTax in 2015, but don't find a 2015 return in your
2015 Tax Timeline? If so, then you likely have multiple accounts and
signed into the wrong one. If you used the desktop version for 2015
(CD/download), then it won't be in an online Tax Timeline.
To get
a list of your User IDs and recover account access, you can use the
tool at the link below. Try using your phone number first. If you try
using your email address, and you have more than 1 email address, you
should run the tool on each one.
NOTE: Before running the
account recovery tool below, log out of all Intuit accounts including
this user forum, or you might end up in a loop. Then clear your browser
Internet cache, close your browser, then reopen it, and go to the link
below. You may wish to copy this link so you can paste it into the new browser session.
https://myturbotax.intuit.com/account-recoveryIf
still no luck after running that on your phone number and each email
address you have, then run the tool yet again, but this time choose the
small blue link that says
"Try something else", and it will look you up by SSN and other parameters.