If you take a distribution from your 401(k) in 2024, you'll receive a 2024 Form 1099-R that you'll need to enter into 2024 TurboTax. If you have no after-tax funds in the 401(k), the Form 1099-R will show that the entire distribution is taxable and will add to your AGI by being included on Form 1040 line 5b.
(If you do have after-tax funds in the 401(k), the distribution will be a proportionate mix of after-tax funds and taxable pre-tax funds. Only the taxable amount adds to your AGI. After-tax funds would generally be those that you explicitly contributed as after-tax funds or resulted from repayment of a defaulted 401(k) loan.)
