When e-filing a 2018 tax return you have to enter the 2017 AGI (Adjusted Gross Income) from your filed 2017 tax return for your electronic signature.
To access your current or prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on View adjusted gross income (AGI)
You can also get free transcripts of your federal return from the IRS which includes the AGI - http://www.irs.gov/Individuals/Get-Transcript
If you filed your 2017 tax return late in 2018 (November or later) or did not file a 2017 tax return, then enter a 0 (zero) for the 2017 AGI. If your tax return continues to be rejected by the IRS then your only other option is to print and mail the tax return.
See this TurboTax support FAQ for the procedure to print a tax return for mailing when using the online editions - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
If your 2018 return was rejected for AGI and you are not able to get your 2017 AGI from last year's tax return, then print, sign and mail your 2018 return instead of e-filing it.
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 and/or your state received the return.
Your 2017 tax return shows your 2017 Adjusted Gross Income (AGI) If you filed a joint return then the AGI is the same for each of you.
Form 1040EZ line 4
Form 1040A line 21
Form 1040 line 37
If you are using the same TT account that you used last year, you should also be able to find this number in your Tax Timeline for 2017
If entering the amount from your 2017 tax return does not work, then try entering “0” instead. If that does not work and you still cannot e-file, then print, sign, and mail your tax return.
You can get a free transcript of your past return from the IRS:
Note: If you filed late or amended your return, your correct 2017 AGI may not be in the system.
Note: If you mail your federal return, you will also need to mail your state return. You will not be able to e-file your state return.