It is not the same for the purposes of the additional deduction.  Please do not report any contributions to your TSP as a separate entry in TurboTax  because they are deducted directly from your paychecks. All you have to do is report your W-2 form as it is, no additional entires are needed.  Your taxable income does not include your TSP contributions on your W-2.  When you look at your W-2, you will notice that your wages subject to federal income (box 1) tax are lower because of your TSP plan contributions (box 12). Since the contributions are not counted in your taxable income to begin with, you do not take a deduction when you file your return.