Since the conversion happened in 2025, you will use the 2025 1099-R (that you will receive at the beginning of next year) to report the conversion.
However, since you made the contribution for the 2024 tax year, you will report that contribution on your 2024 tax return, ensuring Form 8606 shows this nondeductible contribution.
Here are the steps to report the 2024 non-deductible contribution in TurboTax Online, from How do I enter a backdoor Roth IRA conversion?:
"Step 1: Enter the Non-Deductible Contribution to a Traditional IRA
- Go to Deductions & Credits
- On the Your tax break screen, locate and select the Retirement and Investments section, then select Start or Revisit next to Traditional IRA and Roth IRA.
- On the Traditional IRA and Roth IRA screen, check the Traditional IRA box and select Continue.
- On the Is This a Repayment of a Retirement Distribution? screen, select No.
- On the Tell Us How Much You Contributed screen, enter the amount contributed and select Continue.
- On the Did You Change Your Mind? screen, select No, then answer the questions on the following screens.
- When you reach the Choose Not to Deduct IRA Contributions screen:
- Select Yes, make part of my IRA contribution nondeductible.
- Enter the amount you contributed.
- If none of your contributions can be deducted, you won't see the option to make part of it nondeductible. Instead, you will see the message Income Too High To Deduct an IRA Contribution, and the full amount of your contribution will automatically be nondeductible.
- Select Continue.
- On the Your IRA Deduction Summary screen, review the info and select Continue.
