If you cannot finish preparing your 2018 return by October 15, 2019 then yes, you will need to purchase and download the desktop software for 2018 to a full PC or Mac, and your return will have to be printed, signed and mailed. You will not be able to e-file.
If you owe tax due, then you will be subject to late fees and interest. TurboTax will not calculate that; the IRS will calculate any penalties/interest based on when they receive your return and payment, and they will bill you later on.
If you are getting a tax refund then there are no penalties for filing late.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
