What is the data source or calculation method for the traditional IRA basis carryover value on line 3 of Part 1 of the IRA Info Wks?

[jjlucadamo-yahoo]

The value calculated by TurboTax changes when the total value of all IRA is modified. I don't understand why.

[dmertz · Accepted solution]

The calculation is done on Part I of Form 8606.  The basis carryover changes because changes in the year-end value of your traditional IRAs changes the amount of basis that is applied to your 2023 traditional IRA distributions and Roth conversions.