Sometimes you need to go back to the taxpayer and ask him what the code is. Usually I find that it relates to a contribution to a state retirement program.  I have never seen that code relate to a 529 contribution. I think you might need some more information to determine if it is indeed a subtraction. If it is related to a state retirement program then it might be a state pickup amount and that addition is determined on the W-2 worksheet in the federal program.