What does my 2018 AGI have to do with my filing 2019

It helps to protect you by insuring that you have the correct number from the previous year.

The IRS wants your 2018 AGI to verify your identity.

You need your 2018 AGI to efile 2019. The AGI is on 2018 1040 line 7. If you filed a Joint return you use the same AGI for each spouse How to find the AGI.
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The IRS requires your 2018 AGI to verify your identity for e-filing. If you're paper-filing your return, you won't need your AGI because those are manually processed.

There are a few places you can get your 2018 AGI:

• If you filed your 2018 taxes with TurboTax, sign in and go down to Your tax returns & documents. Select View adjusted gross income (AGI).
• If you didn’t file your taxes with TurboTax in 2018, the best place to get last year's AGI is from the 1040 form you filed with the IRS. Look on page 2, line 7. If you filed a 1040NR, it'll be on line 35.
• If you're having trouble locating your 2018 return, the second-best place to get your AGI is from the IRS. You can order a free transcript of your return at the IRS Get Transcript site or you can purchase a full copy of your 2018 return. Both versions will include your AGI.

You won't find your AGI on your W-2 or 1099 form because those forms don't take into account over a dozen above-the-line deductions that go into calculating your AGI.

If you didn't file a 2018 federal tax return (or you haven't filed one yet), enter 0 as your AGI.