Any time you want to. There will not a a 2018 AGI in the system for you so try using zero for the 2018 AGI. If zero will not allow you to e-file 2019, you will hav to print, sign and mail 2019.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
**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.**
