When e-filing your return for the current year, use the AGI from the prior year's originally filed accepted return. For 2020, the AGI is listed on line 11.
The return will reject if the amended AGI amount is used. Do not use amounts from an amended return, a corrected amount from a math error notice, or a changed amount from the IRS.
If you did not electronically file by October 15th, enter $0 as the AGI amount.
During the e-file process the IRS matches their files against what prior year AGI they have on file for your SSN (social security number) and compare it to the number that you enter for your prior year AGI. The numbers must match exactly or the IRS will reject the electronically filed return.