You can use the TurboTax online or desktop software to e-file a 2018 tax return at any time up through October 15, 2019. After that date the 2018 tax return can only be printed and mailed.
The TurboTax online editions shut down after 10/15/19 to make way for the 2019 online editions.
2018 Online - https://turbotax.intuit.com/personal-taxes/online/
2018 Desktop - https://turbotax.intuit.com/personal-taxes/cd-download/
