Turbo Tax allows the deduction for CSRS annuity payments on the Nebraska State Income Tax forms, but doesn't provide instructions for how to provide or what is the requested proof that Nebraska requires. What is proof required and how is it submitted?
This Q has been up all day and none else has ventured a plausible help/answer.....so I'll give it a "reasoned", non-NE non-expert shot.....i.e. I don't have NE tax forms.
If you are e-filing NE, then as long as you properly entered it in the software as a CSA-1099-R, (and NOT as a regular plain 1099-R), then the income from it is probably automatically excluded from NE taxable income by the software. You must keep a paper copy of it, and any other income forms...just in case the NE tax people decide to question it. That does happen occasionally on a random basis.
Also...if E-filing, save a copy of your tax return as a PDF file....and print it all out too, and Save it in your 2024 tax folder (NEVER depend on finding the forms later in your TTX account). That paper copy should include an Electronic Filing Instructions sheet, that "might" tell you if you have to mail anything in.
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If you are filing by mail on paper, you would attach a "copy" of your CSA-1099-R form, and any W-2 (if you have one) and any other forms that happen to show NE withholding on them. Don't forget to sign and date it.