If you are referring to e-filing your return, you do use your 2017 AGI. It does not matter what your filing status is for 2018. Your 2017 AGI is
- On your originally-filed 2017 tax return, form 1040 (Line 37), 1040A (Line 21), 1040EZ (Line 4), 1040NR (Line 36), Form 1040X (Line 1, column A)
