The IRS requires your 2017 AGI for identity verification (if you didn't file in 2017, enter 0 as your AGI) when e-filing, so that is why you are being asked for it when filing your 2018 return.

See more information below about how to find your 2017 AGI from a 2017 TurboTax return. If you do not have access to your prior year return, you can request a free online transcript of your 2017 tax return from the IRS.  The transcript will include your 2017 AGI amount on it.  Use this link:  IRS Get Transcript

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