For 2023, you will have to amend that return to report the nondeductible contribution applicable to that year. For 2024, you can do that for the 2024 contribution and then report the rollover by entering the associated Form 1099-R.
For the backdoor IRA, enter a traditional IRA contribution in the Deductions and Credits section of TurboTax, then Retirements and Investments, then Traditional and Roth IRA Contributions. Indicate that your traditional IRA contribution is non-deductible when asked in the program:
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When you enter the 1099-R form in TurboTax for the rollover of funds to the Roth IRA, you need to first indicate that you moved the money to another retirement account and that you did a combination of rolling over, converting or cashing out the money. Then, enter the amount converted to a ROTH IRA. Later on you need to indicate that you tracked non-deductible contributions to your IRA.
Later in the routine enter the basis (non-deductible contributions) of your traditional IRA at the end of the previous year, and later the value of your traditional IRA at the end of the current year.
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