Roth conversions are taxable on the tax return for the year in which the conversion occurs. The 2024 filing deadline only has relevance to making your 2024 IRA contribution.
Requesting a filing extension changes nothing with regard to these transactions. The deadline for making your 2024 traditional IRA contribution is April 15, 2025 whether or not you request a filing extension.
The traditional IRA contribution made fore 2024 will go on your 2024 tax return. Being nondeductible, it will appear on 2024 Form 8606 Part I.
The amount on line 14 will carry forward to line 2 of your 2025 Form 8606 on which your 2025 traditional IRA contribution will be reported as nondeductible.
The Roth conversion will be reported on your 2025 tax return and will appear on Parts I and II of your 2025 Form 1099-R.
1. The deadline for filing your 2024 tax return is irrelevant to the timing of your Roth conversion.
2. Right now you are filing your 2024 tax return, not your 2025 tax return. As mentioned above, the contribution for 2024 is the only transaction of these that will go on your 2024 tax return
3. You should convert everything in your traditional IRA such that you have no funds in a traditional IRA at the end of 2025. Any slight gains will be taxable on your 2025 tax return.
