...as long as box 2a is not empty and contains a non-zero value...yes then box 2a goes into 16.
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If box 2a is empty or marked as "undetermined" in 2b, then it's the Federally-taxable portion of box 1. Sometimes that is just box 1, but can be lower if there were non-deductible (after-tax) contributions to the retirement plan that issued the 1099-R.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
