@JeffP_MA The stimulus payments are an advance tax credit based on the 2020 federal tax return.
The Recovery Rebate Credit Worksheet used by TurboTax and any other tax preparation software is the same worksheet as required by the IRS to calculate the tax credit. The worksheet requires the use of the 2020 AGI from Form 1040 Line 11.
Go to IRS Form 1040 (2020) Instructions page 59 for the Recovery Rebate Credit Worksheet - https://www.irs.gov/pub/irs-pdf/i1040gi.pdf#page=59
